Network Working Group D. Eastlake 3rd Request for Comments: 1898 CyberCash Category: Informational B. Boesch CyberCash S. Crocker CyberCash M. Yesil CyberCash February 1996
CyberCash Credit Card Protocol Version 0.8
Status of this Memo
This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
Abstract
CyberCash is developing a general payments system for use over the Internet. The structure and communications protocols of version 0.8 are described. This version includes credit card payments only. Additional capabilities are planned for future versions.
This document covers only the current CyberCash system which is one of the few operational systems in the rapidly evolving area of Internet payments. CyberCash is committed to the further development of its system and to cooperation with the Internet Engineering Task Force and other standards organizations.
Acknowledgements
The significant contributions of the following persons (in alphabetic order) to this protocol are gratefully acknowledged:
Bruce Binder, Judith Grass, Alden Hart, Steve Kiser, Steve Klebe, Garry Knox, Tom Lee, Bob Lindenberg, Jim Lum, Bill Melton, Denise Paredes, Prasad Chintamaneni, Fred Silverman, Bruce Wilson, Garland Wong, Wei Wu, Mark Zalewski.
In addition, Jeff Stapleton and Peter Wagner made useful comments on the first version of this memo.
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History
For historic purposes, it should be noted that this document was first posted as an Internet draft, and thus made publicly available, on 8 July 1995.
CyberCash, Inc. of Reston, Virginia was founded in August of 1994 to partner with financial institutions and providers of goods and services to deliver a safe, convenient and inexpensive system for making payments on the Internet. The CyberCash approach is based on establishing a trusted link between the new world of cyberspace and the traditional banking world. CyberCash serves as a conduit through which payments can be transported quickly, easily and safely between buyers, sellers and their banks. Significantly - much as it is the real world of commerce - the buyer and seller need not have any prior existing relationship.
As a neutral third party whose sole concern is ensuring the delivery of payments from one party to another, CyberCash is the linchpin in delivering spontaneous consumer electronic commerce on the Internet.
1.1 System Overview
The CyberCash system will provide several separate payment services on the Internet including credit card and electronic cash. To gain access to CyberCash services, consumers need only a personal computer with a network connection. Similarly, merchants and banks need make only minimal changes to their current operating procedures in order to process CyberCash transactions, enabling them to more quickly integrate safe on-line payments into their existing service offerings. Communications with banks are over existing financial communications networks.
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To get started, consumers download free software from CyberCash on the Internet. This software establishes the electronic link between consumers, merchants and their banks as well as between individuals. To make gaining access to the CyberCash system even easier, CyberCash "PAY" buttons may be incorporated into popular on-line service and software graphical user interfaces so that consumers using these products can easily enter the CyberCash system when they are ready to make payments for goods and services. Consumers need not have any prior relationship with CyberCash to use the CyberCash system. They can easily set up their CyberCash persona on-line.
Transactions are automated in that once the consumer enters appropriate information into his own computer, no manual steps are required to process authorization or clearance transactions through the entire system. The consumer need only initiate payment for each transaction by exercising the pay option on an electronic form. Transactions are safe in that they are cryptographicly protected from tampering and modification by eavesdroppers. And they are private in that information about the consumer not relevant to the transaction is not visible to the merchant.
The CyberCash system pays special attention to security issues. It uses encryption technology from the world's leading sources of security technology and is committed over time to employing new security technologies as they emerge.
1.2.1 Authentication and Persona Identity
Authentication of messages is based on Public Key encryption as developed by RSA. The CyberCash Server maintains records of the public key associated with every customer and merchant persona. It is thus able to authenticate any information digitally signed by a customer or merchant regardless of the path the data followed on its way to the server. The corresponding private key, which is needed to create such digital signatures, will be held by the customer or merchant and never revealed to other parties. In customer software, the private key is only stored in an encrypted form protected by a passphrase.
While the true CyberCash identity of a customer or merchant is recognized by their public/private key pair, such keys are too cumbersome (over 100 hex digits) to be remembered or typed by people. So, the user interface utilizes short alphanumeric ID's selected by the user or merchant for purposes of specifying a persona. CyberCash adds check digits to the requested ID to minimize the chance of accidental wrong persona selection. Persona IDUs are essentially public information. Possession of an persona ID without the corresponding private key is of no benefit in the current system.
Individuals or organizations may establish one or more CyberCash customer personas directly with CyberCash. Thus, an individual may have several unrelated CyberCash personas or share a CyberCash persona with other individuals. This approach provides a degree of privacy consistent with Internet presence generally and with cash transactions specifically. However, persona holders who wish to use a credit card for purchases in conjunction with their CyberCash persona must first meet such on-line identification criteria as the card issuing organization requires.
Control over a CyberCash persona is normally available only to an entity that possesses the private key for that persona. However, a special provision is made to associate an emergency close out passphrase with a CyberCash persona. On receipt of the emergency close out passphrase, even if received over insecure channels such as a telephone call or ordinary email, CyberCash will suspend activity for the CyberCash persona. This emergency close-out passphrase can be stored separately from and with somewhat less security than the
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private key for the persona since the emergency passphrase can not be used to divert funds to others. This provides some protection against loss or misappropriation of the private key or the passphrase under which the private key in kept encrypted. In the cash system, the emergency close-out passpharase may also transfer the persona balance to a designated bank account.
1.2.2 Privacy
Encryption of messages use the Digital Encryption Standard (DES), commonly used in electronic payment systems today. It is planned to superencrypt (i.e., encrypted more than one level) particularly sensitive information, such as PIN numbers, and handle them so that the plain text readable version never exists in the CyberCash system except momentarily, within special purpose secure cryptographic hardware that is part of the server, before being re-encrypted under another key.
The processing of card charges through the CyberCash system is organized so that the merchant never learns the customerUs credit card number unless the merchantUs bank chooses to release this information to the merchant or it is required for dispute resolution. In addition, the server maintains no permanent storage of card numbers. They are only present while a transaction involving that card is in progress. These practices greatly reduce the chance of card number misappropriation.
1.3 Credit Card Operation
Using the CyberCash system for credit card transactions, once price has been negotiated and the consumer is ready to purchase, the consumer simply clicks on the CyberCash "PAY" button displayed on the merchant interface, which invokes the merchant CyberCash software. The merchant sends the consumer an on-line invoice that includes relevant purchase information which appears on the customerUs screen. (See PR1 message.) The consumer adds his credit card number and other information by simply selecting from a list of credit cards he has registered to his CyberCash persona. All this information is digitally signed by the customer's CyberCash software, encrypted, and passed, along with a hash code of the invoice as seen by the customer, to the merchant. (See CH1 message.)
Upon receipt, the merchant adds additional authorization information which is then encrypted, electronically signed by the merchant, and sent to the CyberCash Server. (See CM1 & CM2 messages.) The CyberCash Server can authenticate all the signatures and be sure that the customer and merchant agree on the invoice and charge amount. The CyberCash Server then forwards the relevant information to the
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acquiring bank along with a request on behalf of the merchant for a specific banking operation such as charge authorization. The bank decrypts and then processes the received data as it would normally process a credit card transaction. The bank's response is returned to the CyberCash Server which returns an electronic receipt to the merchant (see CM6 message) part of which the merchant is expected to forward to the customer (see CH2 message). The transaction is complete.
2. General Message Wrapper Format
Version 0.8 of the external format for the encoding of CyberCash messages is described below. CyberCash messages are stylized documents for the transmission of financial data over the Internet.
While there are numerous schemes for sending information over the Internet (HTTP, SMTP, and others), each is attached to a specific transmission mechanism. Because CyberCash messages will need to travel over each of these media (as well as others) a transmission independent mechanism is needed.
2.1 Message Format
CyberCash messages consist of the following components:
1. Header - defines the start of the CyberCash message and includes version information.
2. Transparent Part - contains information that is not private.
3. Opaque Part(s) - contains the financial information in the message and is both privacy protected as well as tamper protected. An opaque part is not present in some messages. When present, the opaque part usually provides tamper protection for the transparent part.
4. Trailer - defines the end of the CyberCash message and includes a check value to enable the receiver to determine that the message has arrived undamaged. Note: this check value is intended only to detect accidental damage to the message, not deliberate tampering.
No null characters (zero value) or characters with the eighth bit on are permitted inside a CyberCash message. "Binary" quantities that might have such byte values in them are encoded in base64 as described in RFC 1521.
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2.2 Details of Format
The header consists of a single line which looks approximately like this
$$-CyberCash-0.8-$$
or like this
$$-CyberCash-1.2.3-Extra-$$
It includes a number of fields separated with the minus character "-"
1. "$$" - the literal string with the initial $ in column 1.
2. "CyberCash" - the literal string (case insensitive)
3. x.y or x.y.z - the version number of the message format. x is the primary version number. y is a subversion number. z, if present, is a subsubversion number.
4. "Extra" - an optional additional alphanumeric string.
5. "$$" - the literal string
Version numbers start at 0.7 and count up. The ".z" is omitted when z is zero. 0.7 and 0.8 are the test and initial shipped version of the credit card system. 0.9 and 1.0 are expected to also incorporate the test and initial shipped versions of the cash facilities as well as improvements to the credit card system.
The "Extra" string is used within secure environments so that one subcomponent can scribble a note to another with minimum overhead. For example, a server firewall could put "HTTP" or "SMTP" here before forwarding the message to the core server within the firewall perimeter.
2.3 Body Parts
The body parts of the message (both transparent and opaque) consist of attribute value pairs in formats that are reminiscent of the standard electronic mail header (RFC822) format. However, there are some differences.
Attribute names start with and are composed predominantly of letters and internal hyphens except that they sometimes end with a hyphen followed by a number. Such a trailing number is used when there is logically an indexed vector of values. Attribute names are
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frequently referred to as labels.
If the label ends with a ":", then RFC822 processing is done. While the existence of trailing white space is significant, all leading white space on continuation lines is stripped. Such lines are wrapped at 64 characters in length, excluding any line termination character(s).
However, if the label is terminated with a ";", this indicates a free-form field where new-line characters and any leading white space, after the initial space that indicates a continuation line, is significant. Such lines should not be wrapped except that, to avoid other processing problems, they are forcibly wrapped at 200 characters.
Blank lines are ignored and do not signify a change to a different mode of line handling.
Another way of looking at the above is as follows: after having found an initial $$ start line, you can treat any following lines according to the first character. If it is alphanumeric, it is a new label which should be terminated with a ":" or ";" and indicates a new label-value pair. If it is a white space character, it indicates the continuation of the value for the preceding new label line. (Exactly how the continuation is processed depends on the label termination character.) If it is "$", it should be the end line for the message. If it is #, it is a comment line and should be ignored. Other initial characters are undefined. (As of this date, no software sends CyberCash messages with # lines but they are convenient for commenting messages stored in files.)
2.4 Transparent Part
The transparent part includes any clear-text data associated with the financial transaction as well as information needed by CyberCash and others to decrypt the opaque part(s). It always includes a transaction field which is the transaction number generated by the requester and which is repeated in the response. It always includes a date field that is the local date and time at the requester and is repeated in the response. In all cases other than an initial registration to establish a persona ID, it includes the requester's persona ID.
On messages bound for the server, there is a "cyberkey:" field that identifies which server public key was used to encrypt the session key.
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2.5 Opaque Part
The opaque part consists of a single block of characters encoded using base64 encoding (see RFC 1521). The data in the opaque section is always encrypted before encoding.
The label "opaque" or "merchant-opaque" precedes the opaque part depending on whether the data was encrypted by the client or merchant software.
On messages inbound to the server, the data to be opaqued is DES CBC encrypted under a random transacton key and then that DES key is RSA encrypted under one of the server's public keys. The RSA encrypted DES key appears as the first part of the base64 encoded field and is not broken out as a separate value in the message. The corresponding outbound reply from the server can simply be DES encrypted under this transaction key as there is enough plain text information to identify the transaction and the customer or merchant will have remembered the transaction key from the inbound message.
A signature is not generally necessary in the opaque part of a reply message. Knowledge of the transaction key is adequate authentication. In order for someone to forge the response, they would have to know the server's private key to be able to get at the transaction key. It is assumed that if anyone tampered with the response opaque part, the probability that it would decrypt to something that would parse is insignificant. (Just the fact that the 8th bit has to be off means a chance of 1 in 2**n where there are n characters and that's ignoring the rest of the formatting.) While someone can tamper with the transparent part, this usually either has no effect or means that the client won't find the transaction key, in which case it's just a particular example of denial of service by damaging a message.
2.6 Trailer
The trailer is intended to close the message and provide a definitive and parseable end of the message.
The trailer consists of several fields separated by "-" as in header.
The transmission checksum is the MD5 has of all printable characters in the version number in the start line and those appearing after the second $$ of the start line and before the first $$ of the trailer line as transmitted. Note that all white space is left out of this hash, including any new-lines, spaces, tabs, carriage returns, etc. The exact label terminators actually used (: or ;) are included as would any # comment line. Note that the optional "Extra" string in the $ start line is not included. The idea is to check correct transmission while avoiding sensitivity to gateways or processing that might change the line terminator sequence, convert tabs to spaces, or the like.
Inbound CyberCash request messages normally have a signature, as described below, of all of the messages fields outside of the signature. This signature is transmitted inside the opaque part of the message. It enables the server to authenticate the source of the message.
Messages from a merchant to a client initiating a purchase sequence have fields signed by the merchant. These fields and this signature are included by the client in the opaque part of their card purchase message to the merchant so that, when all is passed on to the server, it can verify that the client saw the information the merchant intended.
More information on CyberCash signatures and the hash codes they are based on, is given below.
3.1 Digital Signatures
Digital signatures are a means of authenticating information. In CyberCash messages, they are calculated by first taking the hash of the data to be authenticated, as described below, and then encoding the hash using an RSA private key.
Anyone possessing the corresponding public key can then decrypt the hash and compare it with the message hash. If they match, then you can be sure that the signature was generated by someone possessing the private key which corresponded with the public key you used and that the message was not tampered with.
In the CyberCash system, clients, merchants, and the server have public-private key pairs. By keeping the private key secret and registering their public key with the server (for a merchant or client) or publishing their public key or keys (for the server), they can provide high quality authentication by signing parts of messages.
An RSA digital signature is approximately the size of the modulus used. For example, if that is 768 bits long, then the binary digital signature would be 768 bits or 96 bytes long and its base 64 encoding would be 128 bytes.
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3.2 Hash Codes
The hashes used in CyberCash messages are message digests. That is, a non-invertable fingerprint of a message such that it is computationally infeasible to find an alternate message with the same hash. Thus the relatively small hash can be used to secure a larger message. If you are confident in the authenticity of the hash and are presented with a message which matches the hash, you can be sure it is the original message, at least as regards all aspects that have been included in the hash.
The hash is calculated using the MD5 algorithm (see RFC 1321) on a synthetic message. The synthetic message is composed of the labels and values specified in a list for the particular hash. Since the hash is input order dependent, it is essential that the label-value pairs be assembled in the order specified. In some cases, a range of matching labels is specified. For example, "card*" to match card- number, card-expiration-date, and all other labels starting with "card". In such cases, all existing matching labels are used in ascending alphabetic order by ASCII character code.
If a label is specified in a signature list but is not present in the label-value data on which the hash is being calculated, it is not included in the hash at all. That is, even the label and label terminator are omitted from the synthetic message.
Before being hashed, the text of the synthetic message is processed to remove all "white space" characters. White space characters are defined as any with an ASCII value of 32 (space) or less or 127 (rubout) or greater. Thus all forms of new-line/carriage-return and distinctions such as blank lines, trailing spaces, replacement of a horizontal tab character by multiple spaces, etc., are ignored for hash purposes.
MD5 hashes are 16 bytes long. This means that the base 64 encoding of such a hash will be 24 characters (of which the last two will always be padding equal signs).
4. Specific Message Formats
This section describes the formats of the Verison 0.8 CyberCash messages by example with comments. The reader in assumed to be familiar with terms such as "acquirer", "PAN" (primary account number), etc., defined in ISO 8583, and currency designations as defined in ISO 4217. A few fields not relevant to current operations have been removed to simplify this exposition.
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In the following example messages, signatures, hashes, and encrypted sections are fake nonsense text and ids are fictitious.
4.1 Persona Registration and Application Retrieval
The first step in customer use of CyberCash is registering a persona using the customer application. This is done with the R1 message defined below. The CyberCash server responds with the R2 message.
When the customer application learns that it is out of date, it can use the GA1 request message to the server and its GA2 response to download a new signed version of itself.
4.1.1 R1 - registration
Description: This is the initial message sent to create a new CyberCash persona.
##################################################################### signature is of the following fields: transaction, date, cyberkey, type, swversion, content-language, requested-id, email, pubkey
##################################################################### Explanation: content-language is taken from the MIME header field (see RFC1766) and is the language text messages should be generated in. (only en-us implemented at this time. swversion used to check if client application is old.
4.1.2 R2 - registration-response
Description: This message gives the success/failure response to R1.
##################################################################### Opaque Key: Same as session key for R1 for same Transaction and connection (there may be no ID!).
type: registration-response server-date: 19950121100506.nnn requested-id: MyRequestedCCID response-id: CyberCashHandle email: myemail@myemailhost.com response-code: success/failure/etc. pubkey: 0VdP1eAUZRrqt3Rlg460Go/TTs4gZYZ+mvI7OlS3l08BVeoms8nELqL1RG1pVYdDrTsX E5L+wcGCLEo5+XU5zTKkdRUnGRW4ratrqtcte7e94F+4gkCN06GlzM/Hux94 swseverity: fatal/warning [absent if ok] swmessage; Tells CyberApp that it is obsolete. Display this text to the user. [only present if SWSeverity present] message; Free text of the error/success condition. This text is to be displayed to the person by the CyberCash application...
In general this includes: duplicate-id, bad-signature, or ill-formed-registration
##################################################################### Signature is of the following fields: no-signature
##################################################################### Explanation: responseid is used to suggest a unique ID if the failure was due to the requested ID being already in use... If the reason for failure was not due to duplicate ID then this field may be omitted. responseid gives the actual ID with check characters appended if success. swseverity can warn user of old client application or indicate failure due to old or known buggy version.
4.1.3 GA1 - get-application
Description: Used by CyberApp to get an updated version.
##################################################################### Opaque Key: Generated using CyberCash encrypting public key identified in CyberKey.
##################################################################### Signature is of the following fields: no signature
##################################################################### Explanation: There may not be a customer persona so there is no ID. There may not be a customer public/private key pair so there is no signature. The swversion is mandatory so the server can tell what to return.
4.1.4 GA2 - get-application-response
Description: Return success and URL of up to date copy of CyberApp or failure.
type: get-application-response server-date: 19950110102334.nnn response-code: success/failure/etc. message; Text message to be displayed to the user providing more information on the success/failure. swversion: 0.8win application-url: http://foo.cybercash.com/server/0.8WIN.EXE application-hash: lSLzs/vFQ0BXfU98LZNWhQ==
##################################################################### Explanation: application-hash is the MD5 of the binary of the application. application-url & application-hash omitted on failure. swversion is the version being transmitted to the customer.
4.2 Binding Credit Cards
The CyberCash system is design to give the card issuing organization control over whether a card may be used via the CyberCash system. The customer, after having registered a persona with CyberCash as described above, can then bind each credit card they wish to use to their CyberCash persona. This is done via the BC1 message from the customer to their CyberCash server and the BC4 response from the server.
4.2.1 BC1 - bind-credit-card
Description: This is the initial message in the process of binding a credit card to a CyberCash persona.
##################################################################### signature is of the following fields: id, date, transaction, cyberkey, type, swversion, card-number, card-salt, card-expiration-date, card-name, card-street, card-city, card-state, card-postal-code, card-country
##################################################################### Explanation: salt is needed so that the hash stored at the server is less informative. Server just remembers the "prefix" of the card number and the hash of the combined card number and salt. If it just hashed the card number, it would be recoverable with modest
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effort by trying to hash all plausible numbers. We don't want to store the card numbers on the server because it would make the server files too valuable to bad guys.
4.2.2 BC4 - bind-credit-card-response
Description: Indicates that the process of binding a credit card terminated. Returns success or failure.
type: bind-credit-card-response server-date: 19950121100506.nnn swseverity: fatal/warning [absent if ok] swmessage; message about obsoleteness of customer software to be shown to the customer. [only present if SWSeverity present] response-code: success/failure/etc. card-number: 1234567887654321 card-type: visa card-salt: 47562310 card-expiration-date: 01/99 card*: [other card* lines to also be given in CH.1 message] message; Plain text for the user can be multiple lines
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##################################################################### Signature is of the following fields: no-signature
##################################################################### Explanation: All the card* lines can be saved as a blob to be submitted in CH.1. card-expiration-date, card-number, card-salt, and card-type should always be present. Depending on reason for failure, not all fields may be present.
4.3 Customer Credit Card Purchasing Messages
In general, CyberCash involvement in the credit card purchasing cycle starts after the user has determined what they are buying. When they click on the CyberCash payment button, a PR1 message is sent by the merchant to the customer as the body of a message of MIME type application/cybercash.
If the customer wishes to proceed, they respond to the merchant with a CH1. The merchant responds with a CH2 but between the receipt of the CH1 and issuance of the CH2, the merchant usually communicates with the CyberCash server via the CM* messages.
4.3.1 PR1 - payment-request
Description: This message is the first message that is defined by CyberCash in the purchase-from-a-merchant process. The shopping has completed. Now we are at the point of paying for the purchases.
Purchase of 4 pairs "Rocket Shoes" at $39.95 ea. Shipping and handling $5.00
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Total Price: 164.80
Ship to: Wily Coyote 1234 South St. Somewhere, VA 12345 merchant-amount: usd 164.80 accepts: visa:CC001, master:CC001,amex:CC001,JCPenny:VK005,macy:VK006 url-pay-to: http://www.ACME.com/CybercashPayment url-success: http://www.ACME.com/ordersuccess url-fail: http://www.ACME.com/orderfail merchant-signed-hash: a/0meaMHRinNVd8nq/fKsYg5AfTZZUCX0S3gkjAhZTmcrkp6RZvppmDd/P7lboFLFDBh Ec0oIyxWeHfArb3OtkgXxJ7qe0Gmm/87jG5ClGnpBnw0dY7qcJ6XoGB6WGnD $$-CyberCash-End-lSLzs/vFQ0BXfU98LZNWhQ==-$$
##################################################################### Opaque Key: no opaque section
##################################################################### Opaque Section Contents: no opaque section
##################################################################### merchant-signed-hash is the signature under the merchant's private key of the hash of the following fields: type, merchant-ccid, merchant-order-id, date, note, merchant-amount, accepts, url-pay-to, url-success, url-fail
##################################################################### Explanation: This message is signed by the merchant but the customer cannot directly verify this signature. When the payment is made, the Customer includes the signature with the hash (derived by the customer directly) in the payment. If these do not match, the CyberCash will not perform the payment function. accepts: The client software will only recognized single word card name in the accepts field of PR1. For example, MasterCard AmericanExpress are recognized where as Master card American express are not recognized. MasterCard and masterCard are both recognized as master card. Card type followed by key designator. For main line credit cards, this will be a CC*. Client can use or ignore the * number as it chooses. For proprietary card, this will be VK* where * is the CheckFree key to use (1 based). Cards separated by comma,
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key designator follows card type and colon. url-pay-to is where the CH1 should be sent. url-fail and url-success are where the browser should look after failure or success.
4.3.2 CH1 - credit-card-payment
Description: This message represents the presentation of a "credit card for payment".
##################################################################### signature is under client private key of the following fields: type, id, order-id, merchant-ccid, transaction, date, pr-hash, pr-signed-hash, cyberkey, swversion, amount, card*
##################################################################### Explanation: The pr-signed-hash field is the same as the merchant-signed-hash in the PR1 message but has a different name for historic reasons.
4.3.3 CH2 - charge-card-response
Description: Return to customer from a CH1 attempt to pay via credit card. Indicates success/failure.
$$-CyberCash-0.8-$$ type: charge-card-response merchant-ccid: ACME-012 id: myCyberCashID transaction: 78784567 date: 1995121100500.nnn merchant-date: 19950121100505.nnn merchant-response-code: failure/success/etc. pr-hash: 7Tm/djB05pLIw3JAyy5E7A== pr-signed-hash: a/0meaMHRinNVd8nq/fKsYg5AfTZZUCX0S3gkjAhZTmcrkp6RZvppmDd/P7lboFLFDBh Ec0oIyxWeHfArb3OtkgXxJ7qe0Gmm/87jG5ClGnpBnw0dY7qcJ6XoGB6WGnD merchant-message; This is a message to display to the user from the merchant. Can be multiple lines... Is not secure. opaque: [might not be present, see explanation] EDD+b9wAfje5f7vscnNTJPkn1Wdi7uG3mHi8MrzLyFC0dj7e0JRjZ2PmjDHuR81kbhqb nX/w4uvsoPgwM5UJEW0Rb9pbB39mUFBDLPVgsNwALySeQGso0KyOjMxNs1mSukHdOmDV 4uZR4HLRRfEhMdX4WmG/2+sbewTYaCMx4tn/+MNDZlJ89Letbz5kupr0ZekQlPix+pJs rHzP5YqaMnk5iRBHvwKb5MaxKXGOOef5ms8M5W8lI2d0XPecH4xNBn8BMAJ6iSkZmszo QfDeWgga48g2tqlA6ifZGp7daDR81lumtGMCvg== $$-CyberCash-End-7Tm/djB05pLIw3JAyy5E7A==-$$
server-date: 19950121100706.nnn amount: usd 10.00 order-id: 1231-3424-234242 card*: [from successful BC4] response-code: failure/success/etc. swseverity: fatal/warning swmessage; Tells CyberApp that it is obsolete. Display this text to the user. [only present if SWSeverity present] message; Free text of the error/success condition. This text is to be displayed to the customer by the CyberCash application...
##################################################################### Signature is of the following fields: no signature
##################################################################### Explanation: Opaque section optional because the CH1 to the merchant can fail due to bad order-id, date, wrong merchant-ccid, etc., etc. So the server may not be involved at all in which case there is no mechanism for generating a secure opaque section. (It could even be that merchant attempt to contact the server times out.) If transaction makes it through server (via CM*) then Response-Code at top level should mirror response-code to merchant from server. (Hopefully the same as the response-code to customer from server but the merchant can't tell that.) Note that there can be two messages, one from merchant and one from the server.
4.4 Merchant Credit Card Purchasing Messages
The merchant presents credit card purchases, makes adjustments, and the like via the CM* series. In general, the credit card cycle is one of getting authorization for a purchase, then capturing the purchase in a batch for clearance, then performing the clearance. It is also possible to void a capture (i.e., remove an item from a batch), and process credits (returns). (See section 5.1.)
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Authorizations always come from an acquirer via the response to a CM1 or CM2 message. If capture is being performed by the acquirer or some entity between the CyberCash server and the acquirer, this is done via a CM3 or CM2 message depending on the arrangement between the merchant and the entity doing the capture. Returns (credits) are handled via message CM5. Message CM4 is provided for voiding a capture or return before the batch is cleared. CM6 is the message format used for responses to all the other CM* messages.
An MM* series has also been implemented for purely merchant originated CyberCash charges as described in section 3.4.7
Current credit card dispute resolution systems assume that the merchant knows the card number. Thus, to work with these systems, special bypass messages have been set up that allow the merchant to obtain, for a particular transaction, the information that CyberCash otherwise goes to lengths to hide from the merchant. See sections 3.4.8 and 3.4.9. This makes the obtaining os such information by the merchant an auditable event.
Many present day merchants operate in a "terminal capture" mode where the authorizations are captured by the merchant and the merchant later submits the settlement batch. Messages have been defined and are being implemented so that such merchant captured batches can be submitted via CyberCash.
4.4.1 CM1 - auth-only
Description: This message is used by the merchant to perform an authorization operation on the credit card sent in by the customer.
##################################################################### merchant-opaque key is generated from the CyberCash encrypting public key identified in merchant-cyberkey.
Customer opaque section (Opaque) - see CH1.
##################################################################### Opaque Section Contents & Signature: (exactly as in CH1)
merchant-signature is on the following fields: merchant-ccid, merchant-transaction, merchant-date, merchant-cyberkey, type, order-id, merchant-amount, pr-hash, pr-signed-hash, id, transaction, date, cyberkey
Customer Signature: see CH1
##################################################################### Explanation: The merchant signature ensures integrity of the majority of the message. validation of the customer signature ensures that the customer opaque part was not tampered or replaced.
4.4.2 CM2 - auth-capture
Description: Do authorization and actually enters charge for clearance. Message just like CM1 except for different type.
Description: Captures a charge previously authorized. Message is the same as CM1 except that it also has an authorization-code field (which is also included in the signature) and the type is different.
##################################################################### merchant-opaque key is generated from the CyberCash encrypting public key identified in merchant-cyberkey.
Customer opaque section (Opaque) - see CH1.
##################################################################### Opaque Section Contents & Signature: (exactly as in CH1)
##################################################################### merchant-signature is on the following fields: merchant-ccid, merchant-transaction, merchant-date, merchant-cyberkey, type, authorization-code, order-id, merchant-amount, pr-hash, pr-signed-hash, id, transaction, date, cyberkey
##################################################################### Explanation: The merchant signature ensures integrity of the majority of the message validation of the customer signature ensures that the customer opaque part was not tampered or replaced.
4.4.4 CM4 - void
Description: Voids out a charge/return if received before clearance. Message is the same as CM1 except that it also has a retrieval-reference-number field (which is also included in the signature) and the type is different.
##################################################################### Merchant-Opaque key is generated from the CyberCash encrypting public key identified in Merchant-CyberKey.
Customer opaque section (Opaque) - see CH1.
##################################################################### Opaque Section Contents & Signature: (exactly as in CH1)
Explanation: The merchant signature ensures integrity of the majority of the message. Validation of the customer signature ensures that the customer opaque part was not tampered or replaced.
4.4.5 CM5 - return
Description: Reverse a previous charge. Really sort of a negative charge. Message just like CM1 except for different type.
##################################################################### Merchant-Opaque Key: Session key same as that of CM1/2/3/4/5 for same Merchant-Transaction and Merchant-CCID.
Opaque Key: Same customer session key from CH1 passed through CM* for ID and Transaction
type: charge-action-response server-date: 19950121100706.nnn action-code: XXX [per ISO 8583] response-code: failure/success/etc. order-id: 1231-3424-234242 pr-hash: 7Tm/djB05pLIw3JAyy5E7A== pr-signed-hash: 8zqw0ipqtLtte0tBz5/5VPNJPPonfTwkfZPbtuk5lqMykKDvThhO0ycrfT7eXrn/hLUC kXoSctahEVdw1KBJbp0EVr1zVzcN9Aa7m2fJgxNfiisTgIRW+PMaa78rn+Ov retrieval-reference-number: 432112344321 authorization-code: a12323 card-hash: 7Tm/djB05pLIw3JAyy5E7A== { card-prefix: nnxxxx [Returned if merchant is not full-PAN] } or { card-number: 1234567890123456 [Returned if merchant is full-PAN] } expiration-date: 12/34 [always present] merchant-swseverity: fatal/warning merchant-swmessage; Message for merchant about out of date protocol number in $$ start line of merchant message. merchant-message; Free text of the error/success condition. This text is for the merchant from the server... id: myCyberCashID transaction: 78784567 date: 19950121100505.nnn
Opaque (Customer) contents:
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server-date: 19950121100706.nnn amount: usd 10.00 order-id: 1231-3424-234242 card*: [from successful BC4] response-code: failure/success/etc. swseverity: fatal/warning swmessage; Tells CyberApp that it is obsolete display this text to the user. [only present if SWSeverity present] message; Free text of the error/success condition. This text is to be displayed to the customer by the CyberCash application...
##################################################################### Signature is of the following fields: no signature
##################################################################### Explanation: retrieval-reference-number is needed for voids. authorization-code is needed for post-auth-capture. These fields are each only present in the CM6 if they were returned by the bank which depends on what operation was being done. card-prefix is first two and last four digits of card-number. At merchant's bank's discretion the card-number or card-prefix is returned. card-hash is really the hash of the full card number and the salt provided by the customer. card-hash is needed so the merchant can, if they wish, sort customer transactions by card without knowing the card number. card* is the card* fields delivered in the CM* messages being responded to. They appear in alphabetic order. server-date duplicated in customer opaque area for security. {}'s in column one just for clarity of alternatives and do not actually appear in the message. []ed comments appear after some fields.
4.4.7 The MM* Message Series
The CM* message series above is the primary CyberCash credit card purchase system for securely handling charges from CyberCash customers. However, merchants, who are authorized by their acquiring bank to accept such charges, may also receive telephone, mail, and over-the-counter sales. To avoid any necessity for the merchant to have a second parallel system to handle these charges, an MM1 through MM6 message series is defined and has been implemented for these less secure transactions.
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The MM* messages look very similar to the CM* series but the "customer opaque" section is actually signed by the merchant and no separate customer CyberCash ID or prior card binding is required. The MM* message examples are omitted here in the interests of brevity.
4.4.8 CD1 - card-data-request
Description: Used by merchant to get card-number, etc., if information needed by merchant to resolve a dispute.
##################################################################### merchant-opaque key is generated from the CyberCash encrypting public key identified in merchant-cyberkey.
Customer opaque section (Opaque) - see CH1.
##################################################################### Opaque Section Contents & Signature: (exactly as in CH1)
##################################################################### merchant-signature is on the following fields: merchant-ccid, merchant-transaction, merchant-date, merchant-cyberkey, type, password, server-date, order-id, merchant-amount, pr-hash, pr-signed-hash, id, transaction, date, cyberkey
Customer Signature: see CH1
##################################################################### Explanation: [see also CM1 explanation] The merchant may need to know the card involved and other information in order to resolve a disputed transaction. This information is all contained in the original CH1 embedded in the CM1 for the transaction. If the merchant saves the CM1 and other transaction information, they can send this CD1 message to the server. While this reduces the pass through confidentiality of the system, the merchant is then on record as asking for this particular credit card number and excessive CD1's from a merchant can be flagged. password is an extra level of security intended to be manually entered
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at the merchant to authorize the unusual action. Server stores a hash of the merchant-ccid and the password.
4.4.9 CD2 - card-data-response
Description: Respond to CD1 with failure or with success and card data.
card-name: John Q. Public expiration-date: 01/99 merchant-swseverity: fatal/warning merchant-swmessage; Message for merchant about out of date protocol number in $$ start line of merchant message. merchant-message; Free text of the error/success condition. This text is for the merchant from the server... id: myCyberCashID transaction: 78784567 date: 19950121100505.nnn
##################################################################### Signature is of the following fields: no signature.
##################################################################### Explanation: This normally returns selected fields from the decoding of the opaque part of a CH1 as sent to the server in a CD1.
4.5 Utility and Error Messges
A number of utility, status query, and special error reporting messages have also been found necessary in implementing the CyberCash system.
It is desirable to be able to test connectivity, roughly synchronize clocks, and get an initial determination of what client protocol and software versions are accepted. This is done via the P1 client to server message and its P2 server to client response.
Clients need to be able to determine the status of earlier transactions when the client or merchant has crashed during or has suffered data loss since the transaction. Two transaction query messages are defined, TQ1 and TQ2. One just queries and the other also cancels the transaction, if it has not yet completed. The response to both of these messages is a TQ3 response from the server.
Since the system operates in a query response mode, there are two cases where special error messages are needed. If a query seems to be of an undeterminable or unknown type, the UNK1 response error message is sent. If a response seems to be of an undeterminable or unknown type or other serious error conditions occur at the client or merchant which should be logged at the CyberCash server, the DL1 or DL2 diagnostic log message is submitted by the client or merchant in question respectively.
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4.5.1 P1 - ping
Description: Very light weight check that we have connectivity from the customer to the server. Does no crypto to minimize overhead.
$$-CyberCash-0.8-$$ type: ping-response id: myCyberCashID [if present in P1] transaction: 12312313 date: 19950121100505.nnn server-date: 19950121100506.nnn swseverity: fatal/warning [absent if ok] swmessage; Tells CyberApp that it is using an obsolete protocol. Display this text to the user. [only present if SWSeverity present] response-code: success/failure/etc. message; Free text of the error/success condition. This text is to be displayed to the sender
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by their CyberCash application... supported-versions: 08.win, 0.81win, 0.8mac $$-CyberCash-End-7Tm/djB05pLIw3JAyy5E7A==-$$
##################################################################### Explanation: swversion does not appear in P1 for security reasons so swseverity and swmessage appear only if the server can tell that things are old from the $$ header protocol version. supported-versions lets client know as soon as possible what versions are supported and, by implication, which are not. Does not compromise security by having client say what version it is.
4.5.3 TQ1 - transaction-query
Description: Client query to server for Transaction status.
##################################################################### signature is of the following fields: id, date, transaction, cyberkey, type, swversion, begin-transaction, end-transaction
##################################################################### Explanation: This is a client status query of a previous transaction or transactions. begin-transaction and end-transaction can be the same.
4.5.4 TQ2 - transaction-cancel
Description: Client query to server for Transaction cancellation/status.
##################################################################### signature is of the following fields: id, date, transaction, cyberkey, type, swversion, begin-transaction, end-transaction
##################################################################### Explanation: This is a client attempt to cancel a previous transaction or transactions. begin-transaction and end-transaction can be the same.
The transaction-cancel transaction (TQ.2) is defined between the client and the server. This transaction permits the client to query the status of an operation and to stop the operation from occurring if it has not already occurred.
type: transaction-response response-code: success/failure/etc. message; general free form text message from server to customer.... swseverity: fatal/warning swmessage; Message indicating that CyberApp software is obsolete. May be multiple lines. report-fee: usd 0.15 [if non-zero]
##################################################################### Signature is of the following fields: no signature
##################################################################### Explanation: Report-fee is the notification that this report cost a fee and is only present if there is a fee. There can be multiple transaction for the same transaction number as there could have been a auth, post-auth-capture, void, etc.
Terms "original transaction" refers to the payment or other transaction that is being queried or canceled. Note: this transaction may not actually reside at the server. "request" refers to the requesting TQ.2 or TQ.1 message
id: id from the request message date: date from the request message transaction: transaction from the request message
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server-date: current date/time type: transaction-response response-code: response code for request message, can be one of: "success" means the request message was processed. Does not imply query or cancellation status of the request. "failure-hard" means that the request message was not processed due to being ill-formed or otherwise inoperable. "failure-swversion" means that the request message was not processed due to software revision problems. message: the message applies only to the TQ transaction, not to the status of the transactions being queried or canceled. The message is provided according to the response-code as: "success" - message is omitted. "failure-hard" - use standard hard failure message. "failure-swversion" - use standard swversion message for fatal swseverity: applies to request message swmessage: applies to request message -- per query/cancel fields ('N' is a series from 1 to N) -- transaction-N: transaction number of original transaction, or if the original transaction is not present in server the transaction number that the query / cancel request refers to transaction-status-N: status of original transaction, may be one of: "success" the original transaction was successfully processed. If request was TQ.2, cancellation is not performed. "failure" the original transaction was not successfully processed. If request was TQ.2, cancellation is not performed (however, there is nothing to cancel, so it's all the same to the customer app). "pending" the original transaction is still being processed and final disposition is not known. "canceled" the original transaction has been canceled by the server. Later arrival of the original transaction will not be processed, but will be returned with a "failure-canceled" returned. server-date-1: server-date field from original transaction or omitted if original transaction is not present in the server" date-1: date field from original transaction or omitted if original transaction is not present in the server" type-1: type field from original transaction or omitted if original transaction is not present in the server"
4.5.6 UNK1 - unknown-error
Description: This is the response sent when the request is so bad off you can't determine what type it is or the type is unknown to you. Sent from Merchant to Client or from Server to Merchant or from Server to Client.
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##################################################################### Sender: MerchantApp or CyberServer Receiver: CyberApp or MerchantApp ##################################################################### Sample Message:
$$-CyberCash-0.8-$$ type: unknown-error unknown-error-message: Text message of error condition to display to user. (CyberCash wrapper not found, wrapper integrity check fails, unknown protocol version specified, unknown type specified, etc.) { server-date: 19950121100506.nnn [if sent by server] } or { merchant-date: 19950121100506.nnn [if sent by merchant] } x-id: mycybercashID x-transaction: 123123213 x-date: 19950121100505.nnn x-cyberkey: CC1001 x-opaque: 2DqiOQfGRZjzddWpEZwGsJnoTsp9Yiri8DE9cPUMPsJ7lTFuE4XHi4QfN2cAipDB2G/G 9hr7Hj4u4xfMky7nPvJurClZejkI8eNp8iXLtrfS4DhR4yCFQjCiKk0dh83p+DDsFVV7 TI3Du2B15sQS+SdaoPwkfVDnJv4Y+b7vu2cN7bG7exCkBapBcJZbReNaWX5sf+U8ypfw 5V6QdMOzNXpef3z+cTTWfGOtmn9T1Pwo1Yi9ObyIf/wiK+IPb+bBZ9UwLZSB+qVMfJmX GnHXO3AnA/PD+jKYCtsm2Gxv2WB3CuezOyzPtORuqLp5ubgnLBF9aBBjxwLdbn+cp5sm lw51IHbmo1Jj7H6wyNnRpEjy4tM73jcosBfGeQDHxgyH1uaiFNr2D+WvmuYo7eun2dsy Wve2O/FwicWHvkg5aDPsgOjzetsn1JCNZzbW $$-CyberCash-End-7Tm/djB05pLIw3JAyy5E7A==-$$
##################################################################### Opaque Key: see explanation
##################################################################### Opaque Section Contents: see explanation
##################################################################### Signature is of the following fields: see explanation
##################################################################### Explanation: This message is sent as a response when you can't find or understand even the type of a message to you. It will always have type and unknown-error-message fields at the beginning. Any fields from the request that are parseable are simply echoed back in the UNK1
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message with "x-" prefixed to it. Thus, if an x-opaque appears, it was whatever the opaque was in the original request, etc. If you can decrypt the opaque section, you don't want to put the results here in the clear! {}'s in the first column are to group alternatives only and do not appear in the message. Since the customer originates exchanges with merchant and server and merchant originates exchanges with server, this message will only be emitted from the merchant to the customer or the server to the customer or merchant. It should generally just be logged for debugging purposes. You may need to watch out for denial of service via forged or replayed UNK1 messages.
4.5.7 DL1 - diagnostic-log
Description: Client diagnostic log of bad message from either merchant or server.
##################################################################### Explanation: Client application does not expect a response for this message. The decrypted original message will be in the opaque section unless decryption fails. If decryption fails then un-decrypted opaque in the original will be sent. This message will be sent to a different script or socket or host than normal messages so that it will just be absorbed and never generate an UNK1 response or anything, even if this message itself is screwed up.
4.5.8 DL2 - merchant-diagnostic-log
Description: Merchant diagnostic log of bad message from server.
##################################################################### Explanation: Merchant application does not expect a response for this message. The decrypted original message will be in the opaque section unless decryption fails. If decryption fails then un-decrypted message will be sent. This message will be sent to a different script or socket or host than normal messages so that it will just be absorbed and never generate an UNK1 response or anything even if this message itself is screwed up.
4.6 Table of Messages Described
The following 31 messages are described in this document.
C = Customer App, M = Merchant App, S = CyberCash Server
CyberCash is extending the facilities available through the CyberCash system. We are committed to implementing a full cash system, including efficient transfer of small amounts of money, the extension of the credit card system to handle terminal capture and clearances, and other improvements.
5.1 The Credit Card Authorization/Clearance Process
There are six steps in credit card processing as listed below. The first four are always involved if a transacation is completed. The fifth and sixth are optional.
(1) authorization: merchant contacts their acquiring back which normally contacts the card issung bank and returns to the merchant an approval/guarantee or a disapproval. This
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temporarily decreases the available credit on the card. (2) capture: the charge information for a purchase is entered by the merchant into a batch. (3) clearance: a batch of items is processed. This actually causes the items in the batch to appear on credit card statements as sent by the issuing bank to its carholders. (4) settlement: the actual interbank transfer of net funds. (5) void: the merchant undoes step 2 (or 6) and causes a charge (or credit) to be removed from a batch. Must be done before the batch is processed. (6) credit: the merchant causes a "negative charge" or credit to be entered into a batch. This will appear on the cardholders statement.
The fourth step, settlement, is entirely within the banking community and does not concern us here. CyberCash 0.8 provides messages to do 1, 1&2, 2, 5, and 6. This is adequate for credit card processor systems where the batch is accumulated at the bank or between the bank and the merchant. CyberCash 0.8 supports such "host capture" systems. Other credit card processor systems require the merchant to accumulate the batch. Such systems are frequently referred to as "terminal capture". This makes actions 2, 5, and 6 internal to the merchant but requires messages to perform action 3. Such batch clearance messages will be included in future versions of the CyberCash merchant and server software.
5.2 Lessons Learned
The continuing rapid development of the CyberCash system is an interesting experience. The system must deal with many existing browsers and legacy banking systems. Existing credit card processors that convey transactions to acquiring banks have complex and varied interfaces. The sophistication of security attacks on the Internet is growing rapidly.
In the face of such a rapidly changing environment, it was essential to adopt a general message framework so that messages and fields could be added as they were found necessary. Any attempt to reduce the system to a small number of perfectly opimized messages in advance would have doomed the system to failure. (As of mid-October 1995, the total number of CyberCash messages defined, including those planned for cash and microcash, enhancements to the credit card system, and some old messages being phased out in favor of improved replacements, is just over a hundred.)
Flexible operational and error handing facilities are also, as usual, the bulk of the system. Version numbering and tracking has proved to be quite important and merchant versioning is being added.
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Use of text for messages has proven very beneficial. This makes it possible to easily deal with messages using common everyday tools such as text editors and spead sheets. Use of binary TLV (type, length, value) encoding or the like is certainly possible but imposes a significantly higher level of complexity on every tool that has to deal with the messages.
Encryption and decryption impose some difficulties in development. Any confusion about decryption keys or algorithms will render encrypted material meaningless and tools are needed to provide decyrption for debugging outside of normal program operation. But this pales compared with the stringencies imposed by signatures. All parts of the system must have absolutely identical ideas as to the exact bit patterns to be hashed or signed and their exact order. Seemingly trivial differences in capitalization, punctuation, framing, order, or the like, in addition to any disagreement about keys or algorithms, will lead to frustrating failures of signatures to match. Passing signatures through an intermediate system and checking them at a third system, as is done when a customer's signature is passed through a merchant and checked at the CyberCash server, compounds the problem.
6. Security Considerations
The CyberCash Version 0.8 Credit Card system provides substantial protection to payment messages as described above in sections 1.2, 2.2.4, and 2.2.5. However, it provides no privacy to the shopping interaction which is essentially outside of its purview. It also provides no protection against dishonest merchants other than those normally available with credit card purchases. Care must be taken to avoid loss of control of the machines on which parts of this system runs or security may be compromised.
Current credit card dispute resolution systems require deliberate bypasses be implemented for some of the security normally established by CyberCash as described in section 3.4.
References
[ISO 4217] - Codes for the representation of currencies and funds
[RFC 822] - Crocker, D., "Standard for the format of ARPA Internet text messages", STD 11, RFC 822, UDEL, August 1982.
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[RFC 1521] - Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft, September 1993.
[RFC 1766] - Alvestrand, H., "Tags for the Identification of Languages", UNINETT, March 1995.
Authors' Addresses
Donald E. Eastlake 3rd CyberCash, Inc. 318 Acton Street Carlisle, MA 01741 USA
Phone: +1 508 287 4877 EMail: dee@cybercash.com
Brian Boesch CyberCash, Inc. 2100 Reston Parkway, Suite 430 Reston, VA 22091 USA
