FORMAT-PRESERVING CRYPTOGRAPHIC SYSTEMS

• US 20100111297A1
• Filed: 04/29/2009
• Published: 05/06/2010
• Est. Priority Date: 05/02/2008
• Status: Active Grant

• Current Assignee: Micro Focus LLC (Open Text Corporation)
• Original Assignee: Voltage Security Incorporated (HP Inc.)
• Inventors: Pauker, Matthew J., Spies, Terence
• Granted Patent: US 8,208,627 B2
• Time in Patent Office: Days
• US Class Current: 380/37
• CPC Class Codes: H04L 2209/24 Key scheduling, i.e. generating round keys or sub-keys for block encryption
• CPC Class Codes: H04L 9/0625 with splitting of the data block into left and right halves, e.g. Feistel based algorithms, DES, FEAL, IDEA or KASUMI

Abstract

Format-preserving encryption and decryption processes are provided. The encryption and decryption processes may use a block cipher. A string that is to be encrypted or decrypted may be converted to a unique binary value. The block cipher may operate on the binary value. If the output of the block cipher that is produced is not representative of a string that is in the same format as the original string, the block cipher may be applied again. The block cipher may be repeatedly applied in this way during format-preserving encryption operations and during format-preserving decryption operations until a format-compliant output is produced. Selective access may be provided to portions of a string that have been encrypted using format-preserving encryption.

Claims

1. A method for performing encryption at computing equipment, comprising:

obtaining an encoded binary value representing an unencrypted string in a given format;

applying a block cipher to the encoded binary value to produce a block cipher output;

after each application of the block cipher, determining whether the block cipher output is representative of a string in the given format; and

whenever it is determined that the block cipher output is not representative of a string in the given format, applying the block cipher an additional time to update the block cipher output.

2. The method defined in claim 1 further comprising:

when it is determined that the block cipher output is representative of a string in the given format, processing the block cipher output to produce an encrypted version of the unencrypted string.

3. The method defined in claim 2 wherein processing the block cipher output comprises converting the block cipher output from binary to characters.

4. The method defined in claim 2 wherein processing the block cipher output comprises restoring removed string elements to the encrypted version of the unencrypted string.

5. The method defined in claim 2 wherein obtaining the encoded binary value comprises:

obtaining the unencrypted string in the given format; and

encoding the unencrypted string to produce the encoded binary value.

6. The method defined in claim 5 wherein encoding the unencrypted string to produce the encoded binary value comprises encoding the string as a unique binary value.

7. The method defined in claim 6 wherein encoding the unencrypted string comprises converting the string to numeric values and multiplying the numeric values by coefficients.

8. The method defined in claim 7, wherein a given one of the coefficients is associated with a given character in the string, the method further comprising computing the given one of the coefficients by computing a product of a set of numbers each of which represents how many possible character values are associated with a respective character in the string prior to the given character.

9. A method for performing decryption at computing equipment, comprising:

obtaining an encoded binary value representing an encrypted string in a given format;

applying a block cipher to the encoded binary value to produce a block cipher output;

after each application of the block cipher, determining whether the block cipher output is representative of a string in the given format; and

whenever it is determined that the block cipher output is not representative of a string in the given format, applying the block cipher an additional time to update the block cipher output.

10. The method defined in claim 9 further comprising:

when it is determined that the block cipher output is representative of a string in the given format, processing the block cipher output to produce a decrypted version of the encrypted string.

11. The method defined in claim 10 wherein processing the block cipher output comprises converting the block cipher output from binary to characters.

12. The method defined in claim 10 wherein processing the block cipher output comprises restoring removed string elements to the decrypted version of the encrypted string.

13. The method defined in claim 10 wherein obtaining the encoded binary value comprises:

obtaining the encrypted string in the given format; and

encoding the encrypted string to produce the encoded binary value.

14. The method defined in claim 13 wherein encoding the encrypted string to produce the encoded binary value comprises encoding the encrypted string as a unique binary value.

15. The method defined in claim 14 wherein encoding the encrypted string comprises converting the string to numeric values and multiplying the numeric values by coefficients.

16. The method defined in claim 15, wherein a given one of the coefficients is associated with a given character in the string, the method further comprising computing the given one of the coefficients by computing a product of a set of numbers each of which represents how many possible character values are associated with a respective character in the string prior to the given character.

17. A method for using at least first and second cryptographic keys to provide at least first and second users with selective access to the contents of a string, comprising:

with format-preserving encryption, encrypting a first plaintext part of the string using the first cryptographic key to produce first ciphertext that is in the same format as the first plaintext part while leaving a second plaintext part of the string unencrypted; and

with format-preserving encryption following encryption of the first plaintext part of the string, encrypting both the second plaintext part of the string and the first ciphertext to produce second ciphertext, wherein the second ciphertext is in the same format as the string.

18. The method defined in claim 17 further comprising:

providing the first and second keys to the first user; and

providing the second key to the second user without providing the first key to the second user.

19. The method defined in claim 18 further comprising:

at the second user, decrypting the second ciphertext for the second user to produce the first ciphertext part and the second plaintext part.

20. The method defined in claim 19 further comprising:

at the first user, decrypting the first ciphertext part to produce the first plaintext part.

21. The method defined in claim 20 wherein the decrypting the first ciphertext part comprises decrypting the first ciphertext part using a block cipher.