Timing attacks against user logon and network I/O

• US 20050044390A1
• Filed: 09/08/2004
• Published: 02/24/2005
• Est. Priority Date: 05/03/1999
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Trostle, Jonathan T.
• Granted Patent: US 7,644,439 B2
• Time in Patent Office: Days
• US Class Current: 713/188
• CPC Class Codes: G06F 21/55 Detecting local intrusion or implementing counter-measures
• CPC Class Codes: G06F 21/83 input devices, e.g. keyboards, mice or controllers thereof

Abstract

In a first aspect of the invention, method for classifying characters within a character string entered via a keyboard device includes logging interrupts, checking a time between interrupts, checking an interrupt duration and classifying the characters within the character string based upon the time between interrupts and the interrupt duration. In a second aspect of the invention, a method for protecting against timing attacks against a trusted path mechanism includes employing a multithreaded process with a first thread to prevent any timing Trojan horses from running, running the first thread in a loop at a first priority and preventing unprivileged processes from obtaining a priority higher than the first priority.

Claims

1. A method for classifying characters within a character string, comprising:

logging interrupts;

checking a time between interrupts;

checking an interrupt duration; and

classifying the characters within the character string based upon said time between interrupts and said interrupt duration.

2. A method for determining whether consecutively entered keyboard characters are from the same timing equivalence class, comprising:

determining a cache miss average time;

determining a cache hit average time;

determining a threshold based upon said cache miss average time and said cache hit average time;

reading a first character;

clearing cache after said reading a first character;

reading a second character after said clearing cache;

determining a processing time for said reading a second character; and

indicating whether said first character and said second character are from the same timing equivalence class based upon said threshold and said processing time.

3. A method for determining whether consecutively entered keyboard characters are from the same timing equivalence class, comprising:

reading a first character;

clearing cache after said reading a first character;

reading a second character after said clearing cache;

determining a processing time for said reading a second character; and

indicating whether said first character and said second character are from the same timing equivalence class based upon a predetermined threshold and said processing time.

4. A method for classifying characters within a character string, comprising:

determining a first classification of a plurality of characters based on a first character string application processing time;

determining a second classification of said plurality of characters based on a second character string application processing time; and

determining a third classification of said plurality of characters based upon the combination of said first classification and said second classification.

5. A method for identifying the equivalence class of consecutively entered keyboard characters in an n-character string, comprising:

clearing a cache after character n-l is read;

testing each equivalence class to determine which equivalence class includes character i; and

identifying the equivalence class of characters in a string comprising characters 1 to n-1.

6. A method for protecting against timing attacks against a trusted path mechanism, comprising:

requiring computer user passwords comprising at least twenty-eight characters;

selecting said password characters such that at most one character is within eight keys of the number one (“

1”

) key; and

selecting said password characters such that at most one character is within eight keys of the forward slash (“

/”

) key.

7. The method of claim 6 wherein said computer is a UNIX system.

8. A method for protecting against timing attacks against a trusted path mechanism, comprising:

requiring new computer user passwords at least every two months; and

enforcing a relatively strong password policy.

9. The method according to claim 8 wherein said new computer passwords differ from the corresponding old computer passwords by at least two characters.

10. A method for protecting against timing attacks against a trusted path mechanism, comprising:

configuring a computer system for Trojan horse non-persistence; and

enforcing a relatively strong password policy.

11. The method according to claim 10 wherein:

said computer system comprises a UNIX computer system;

said password policy comprises requiring computer passwords comprising at least ten characters; and

said method further comprises rebooting said computer system at least once a day.

12. A method for protecting against timing attacks against a trusted path mechanism, comprising:

modifying a trusted path mechanism implementation to be a multithreaded process comprising a first thread to prevent any timing Trojan horses from running, said first thread running in a loop at a relatively high priority.

13. The method according to claim 12, said method further comprising:

clearing cache before completing the trusted path mechanism.

14. A method for protecting against timing attacks against a trusted path mechanism, comprising:

employing a multithreaded process comprising a first thread to prevent any timing Trojan horses from running;

running said first thread in a loop at a first priority; and

prohibiting unprivileged processes from obtaining a priority higher than said first priority.

15. The method according to claim 14, said method further comprising:

clearing cache before completing the trusted path mechanism.

16. The method according to claim 15 wherein said computer system comprises a UNIX computer system.

17. A method for protecting against timing attacks against a trusted path mechanism, comprising:

employing a network user authentication protocol including a public key algorithm.

18. The method according to claim 17, further comprising:

requiring computer user passwords having at least eight characters.

19. A method for protecting against timing attacks against a trusted path mechanism, comprising:

encrypting a computer user private key in a password;

storing said computer user private key on a tamper-proof smart card; and

issuing a tamper-proof smart card containing a computer user private key to each computer user.

20. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to classify characters within a character string, comprising:

a first module comprising code for causing a machine to log interrupts;

a second module comprising code for causing a machine to check a time between interrupts;

a third module comprising code for causing a machine to check an interrupt duration; and

a fourth module comprising code for causing a machine to classify the characters within the character string based upon said time between interrupts and said interrupt duration.

21. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to determine whether consecutively entered keyboard characters are from the same timing equivalence class, comprising:

a first module comprising code for causing a machine to determine a cache miss average time;

a second module comprising code for causing a machine to determine a cache hit average time;

a third module comprising code for causing a machine to determine a threshold based upon said cache miss average time and said cache hit average time;

a fourth module comprising code for causing a machine to clear cache after reading a first character;

a fifth module comprising code for causing a machine to read a second character after said clearing cache;

a sixth module comprising code for causing a machine to determine a processing time for said reading a second character; and

a seventh module comprising code for causing a machine indicate whether said first character and said second character are from the same timing equivalence class based upon said threshold and said processing time.

22. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to determine whether consecutively entered keyboard characters are from the same timing equivalence class, comprising:

a first module comprising code for causing a machine to read a first character;

a second module comprising code for causing a machine to clear cache after said reading a first character;

a third module comprising code for causing a machine read second character after said clearing cache;

a fourth module comprising code for causing a machine to determine a processing time for said reading a second character; and

a fifth module comprising code for causing a machine indicate whether said first character and said second character are from the same timing equivalence class based upon a predetermined threshold and said processing time.

23. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to classify characters within a character string, comprising:

a first module comprising code for causing a machine to determine a first classification of a plurality of characters based on a first character string application processing time;

a second module comprising code for causing a machine to determine a second classification of said plurality of characters based on a second character string application processing time; and

a third module comprising code for causing a machine to determine a third classification of said plurality of characters based upon the combination of said first classification and said second classification.

24. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to identify the equivalence class of consecutively entered keyboard characters in an n-character string, comprising:

a first module comprising code for causing a machine to clear a cache after character n-l;

a second module comprising code for causing a machine to test each equivalence class to determine which equivalence class includes character n; and

a third module comprising code for causing a machine to identify the equivalence class of characters in a string comprising characters 1 to n-l.

25. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to protect against timing attacks against a trusted path mechanism, comprising:

a first module comprising code for causing a machine to require computer user passwords comprising at least twenty-eight characters;

a second module comprising code for causing a machine to select said password characters such that at most one character is within eight keys of the number one (“

1”

) key; and

a third module comprising code for causing a machine to select said password characters such that at most one character is within eight keys of the forward slash (“

/”

) key.

26. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to protect against timing attacks against a trusted path mechanism, comprising:

a first module comprising code for causing a machine to modify a trusted path mechanism implementation to be a multithreaded process comprising a first thread to prevent any timing Trojan horses from running, said first thread running in a loop at a relatively high priority.

27. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to protect against timing attacks against a trusted path mechanism, comprising:

a first module comprising code for causing a machine to employ a multithreaded process comprising a first thread to prevent any timing Trojan horses from running; and

a second module comprising code for causing a machine to run said first thread in a loop at a first priority; and

a third module comprising code for causing a machine to prohibit unprivileged processes from obtaining a priority higher than said first priority.