Telephone tone security device5818937Abstract An encryption device. A user wishes to identify himself to a remote party, over a telephone line. The remote party provides a Transaction Number, TN, to the user. The TN is given to the encryption device. The user gives the encryption device a Personal Identification Number, PIN. The encryption device generates a random number, combines it with the PIN and TN, to form an Authorization Number, AN, and encrypts the AN into cypher text. The cypher text is transmitted to the remote party, together with the user's name. The remote party de-crypts the cypher text, to obtain the TN and PIN. Using the name received from the user, and a table of names, and their associated PINs, the remote party verifies whether the PIN obtained from the AN matches the PIN assigned to the name given by the user. If so, the user's identity is considered verified, but without requirement that the user disclose a PIN, in plain text form, over a telephone. Claims I claim: Description BACKGROUND OF THE INVENTION
TABLE
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Public key:
N -- a product of two prime numbers, P and Q.
P and Q are maintained in secrecy.
e -- a number relatively prime to the product
(P - 1) .times. (Q - 1).
Private key:
d = e.sup.-1 (MOD(P - 1) .times. (Q - 1)).
(The expression "i MOD j" refers to the
positive remainder when i is divided by
j.)
Encryption process:
c = m.sup.e (MOD N)
"m" is the plain-text message.
"c" is the cypher text.
De-cryption process:
m = c.sup.d (MOD N)
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As the Table indicates, the public key contains two parts, N and e. These are both made publicly available. For example, every bank issuing a credit card may publish its own public key. The publication can be done in a manner which allows remote downloading. For instance, a customer, such as caller 2 in FIG. 2, can dial a toll-free telephone number which transmits, in DTMF format, the public key of the bank. A private key, d, exists, which is not public, but is known only to the verifier. The caller does not know the private key. EXAMPLE An example will illustrate the encryption-decryption process. Assume P=47 and Q=71. Then N=P.times.Q=3337. Select the public key e, at random, to be 79. The public key e must contain no factors in common with (P-1).times.(Q-1)=46.times.70=3220. Based on the foregoing, d=79.sup.-1 (MOD 3220)=1019. The result of 1019 can be justified by rearrangement: d=1019=79.sup.-1 (MOD 3220) 1019.times.79=1(MOD 3220)=80,501 80,501/3220=25+1/3220 Since the remainder (ie, 1/3220) when multiplied by 3220, is unity, the original statement is confirmed. At this point, the public key and the private key have been computed. Assume the plain-text authorization number, AN, is 668. The AN is encrypted according to the following expression: 688.sup.79 (MOD 3337)=1570. The cypher text is thus 1570. This number is transmitted to the verifier, as in FIG. 4B. De-cryption by the verifier is done according to the following expression: 1570.sup.1019 (MOD 3337)=688. The plain-text AN, 668, is thus recovered. For longer AN's, the AN can be broken into groups of small numbers, such as breaking the AN of 668243550 into three groups: 668, 243, and 550. Each group is encrypted separately. Breaking a large AN into small groups eliminates the step of raising a large AN to a large power, as required in computing c, the cypher text, in the Table. Raising a large number to a large power can cause computational difficulties in some computers. Other encryption and de-cryption techniques, in addition to that discussed above, are discussed in Applied Cryptography, Protocols, Algorithms, and Source Code in C, Chapter 19, by Bruce Schneier, John Wiley & Sons, New York (1994). Perhaps the leading journal article on public-key cryptography is W. Diffie and M. Hellman, "New Directions in Cryptography," IEEE Transactions on Information Theory, Vol. IT-22, No. 6, November, 1978. The preceding two references are hereby incorporated by reference, with the Schneier book being incorporated in its entirety. The following U.S. patents are hereby incorporated by reference:
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4,944,007 Austin July 24, 1990
4,689,478 Hale August 25, 1987
4,634,845 Hale January 6, 1987
4,405,829 Rivest September 20, 1983
4,424,414 Hellman January 3, 1984
4,200,770 Hellman April 29, 1980
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Additional Considerations 1. FIG. 5 illustrates one architecture of the TTSD, which contains a microprocessor 30 and memory 33. The latter contains programs which control operation of the TTSD, and perform the tasks discussed above. The memory 33 also stores the public keys, including those permanently loaded at the time of manufacture, as described below, in point 5, and those loaded later. The microprocessor 30 also generates the random number RN, shown in FIG. 2C. Memory 33 also stores the TN and PIN which are temporarily loaded, for each transaction. Modem 36 (which can be replaced by a DTMF encoder/decoder), allows transmission and reception of data. A serial port 39 can also be used for import and export of data. A speaker 41 and a microphone 44 allow the communication with a telephone handset, illustrated in FIGS. 6A and 6B, and described in point 2, below. A digital-to-analog converter, D/A in FIG. 5, drives the speaker 41, and an analog-to-digital converter A/D is driven by the microphone 44. Additional features shown in FIG. 5 will be explained below. 2. The TTSD may take the form of a hand-held unit, as in FIG. 1, which communicates acoustically with a telephone handset 39, as indicated in FIGS. 6A and 6B. In FIG. 6A, the TTSD transmits information to the handset. In FIG. 6B, the TTSD receives information from the handset. Acoustical shields 40 in FIG. 6C, resembling the fluid-filled muffs contained on radio headsets used by aircraft pilots, can be used to block external noise, to improve acoustic coupling between the TTSD and the handset. The TTSD may also be wired into the telephone line itself, as in FIG. 6D. In this case, it is possible for the TTSD to obtain its operating power from the telephone line itself, indicated by arrow 49 in FIG. 5, as by implementing it using low-power CMOS circuitry. As an alternate, it may be desirable to splice into the cord 41 of the handset 39 of FIG. 6D. 3. It is preferred that the public key be downloadable into the TTSD with a minimum of user involvement, as by following this procedure: First, a user, in pursuit of a public key, dials an appropriate telephone number. Next, a system answers the call, and prompts the user to select the public key desired. In response, the system downloads the public key selected to the TTSD, which receives the information in one of the modes shown in FIG. 6. In principle, this downloading is no different from downloading a file from a public computer service, such as the INTERNET. Alternately, rather than responding to a request by a caller, the system can continually broadcast a public key. As an analogy, the U.S. Naval Observatory, at telephone number 303-499-7111, continually broadcasts the time-of-day. Any number of telephone callers can connect with the Observatory at once, and all callers hear a single recording of a voice, announcing the current time. Of course, if a given caller connects with the Observatory in the middle of a time announcement, the caller simply waits for the next full announcement. The analogous TTSD public key system can repeatedly broadcast the public key. Each broadcast of a public key is preceded by a separator code. When a TTSD connects with the system, the TTSD may connect in the middle of a broadcast of a public key. The TTSD waits for the separator code, and then copies the key which follows. If more than one key is broadcast, different separator codes can be transmitted between keys, giving the identity of the subsequent code. As another alternate, the public keys can be published in newspapers, in bar-code form. The TTSD can be equipped with a bar-code reader 65 in FIG. 5, which reads the bar codes. In the general case, loading a public key is a data-transfer operation, and such operations are well known. 4. Significantly, the TTSD contains no secret information. It is a generic product, publicly available. Successful use only requires entry of a secret PIN, and possibly a TN, at the time a transaction is undertaken. 5. It is possible that a given public key will never be changed, or changed rarely. Thus, since the public key (a) is publicly available and (b) will be rarely changed, it can be treated as a fixed, constant number. It may be permanently stored within the TTSD, along with other public keys, at the time of manufacture. Such memory can be permanently non-volatile, as by using fusible read-only memory, ROM, in which metallic traces are physically melted, in order to store data. Alternately, such memory can be non-volatile, but alterable, such as EEPROM (Electrically Erasable Programmable Read Only Memory) provides. EEPROM is non-volatile, in the sense that it does not require electric power to maintain stored data. But, unlike fusible ROM, the stored data can be changed in EEPROM. To accommodate addition of other public keys, additional memory space is made available, as in FIG. 5, which can be loaded in the manner described above. 6. Ease-of-use is an important attribute of many products. In one form of the invention, the user is completely non-involved with locating a public key, and with loading the public key into the TTSD, as described above. Instead, the verifier 6 or merchant 3 in FIG. 2 is charged with maintaining a necessary supply of public keys, because these parties are expected to have more convenient access to the public keys. When a caller 2 contacts a merchant 3, the merchant transmits the public key to the caller, along with the transaction number TN of FIG. 2A. That public key is used in the encrypting step illustrated in FIG. 4A. 7. In a simplified form of the invention, only the PIN is encrypted using the public key. That is, the cypher text AN(ENCRYPTED) of FIG. 4A contains only the PIN. In another form of the invention, both the PIN and the transaction number, TN, are encrypted using the public key. No random number is used as padding. That is, the cypher text AN(ENCRYPTED) of FIG. 4A contains only the PIN and the TN. 8. Even though the Table indicates that the public key contains two numbers, N and e, it is common usage to refer to these numbers as a single "key." 9. It is not necessary that an actual human being operate the TTSD. Computers, or intelligent agents, can deliver the PIN to the TTSD. 10. In another form of the invention, a microcomputer in FIG. 7, such as the well known Personal Computer, PC, is used. Software 50 contained within the PC controls a modem 55, which retrieves the public keys from remote sources. The software contacts the merchant 3 in FIG. 2, and retrieves the transaction number TN. The software prompts the user, as by a message on the PC's display, to enter the user's PIN. The software encrypts the TN and the PIN, and performs the other steps described above. 11. The term "PIN" was used above, which is an acronym for "Personal Identification Number." A PIN is not required to be literally a number, but, in the general case, can be any sequence of symbols. 12. It should be observed that encoding a word spelled in English letters, such as a name, or an Arabic number, such as "14," into ASCII code does not amount to "encryption." One reason is that translating the ASCII code into human-intelligible form is utterly straightforward. Another reason is that encoding into ASCII code does not conceal anything. 13. It was stated above that modem transmission can be used. Voice-modems are available, which allow voice communication to accompany data transmission, and can be used to allow voice entry of some information (such as PINs) and automated entry of other information (such as TNs, by a computer program). 14. The name of the caller, indicated in FIG. 4B, can be spoken to the merchant 3, or can be encrypted into the cypher text. In the latter case, the format of the cypher text will be modified from that of FIG. 3, in order to accommodate the presence of the name. 15. In the apparatus of FIG. 6D, the telephone user should remain silent while the TTSD transmits the cypher text. This silence can be enforced by a switch 60 which disconnects the telephone 57 from the telephone line, during the transmission of cypher text. The switch 60 can be manually actuated by the user, in which case the switch can be springloaded, so that the disconnection only occurs so long as the switch is depressed by the user. Alternately, the switch 60 can be controlled by the processor 30 in FIG. 5, which disconnects the telephone 57 during transmission of the cypher text. Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.
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