Cryptography & SecurityPresented April 16, 2010

By Dave Stycos, Zocalo Data Systems

Classes of Encryption

• Symmetric Encryption

• Hashing

• Random Number Generation

• Asymmetric Encryption (Public Key)

Symmetric Algorithms• Use a secret key to both encrypt and decrypt

• Are fast

• Operate on fixed-size blocks (8 or 16 bytes)

• DES, Triple-DES, AES, RC4, Blowfish

Symmetric Modes

• Electronic Code Book (ECB)

• Cipher Block Chaining (CBC)

• Output Feedback (OFB)

• Cipher Feedback (CFB)

• Counter (CTR)

• More …

Electronic Code Book (ECB)

Encrypted Using ECB Mode

Cipher Block Chaining (CBC)

Encrypted Using CBC Mode

Initialization Vector

• Not secret

• Must be unique for each stream or file.

• Reused IVs reveal patterns in the first blocks of ciphertext.

Common File Headers

• PDFs %PDF-1.3

• JPEG JFIF

• EXE MZ

Therefore, IVs must be unique for each key!

CBC Weaknesses

• One bad block corrupts the chain

• Only sequential access

• Unsuitable for stream ciphers

Block vs. Stream Ciphers

• Block Ciphers

– Operate on data of known, finite size

– Files, hard drives

• Stream Ciphers

– Operate on data of unknown, indefinite size

– Network flow, media

Cipher Feedback (CFB)

• Symmetric cipher is a pseudo-random number generator.

• Plaintext XOR’ed with PRN, not encrypted by cipher.

Counter (CTR)

Common Weaknesses

• Key Secrecy

• Key Quality

What Is Key Quality?

• Computational infeasibility of brute-force attack

What Is Key Quality?

• Computational infeasibility of brute-force attack

• DES Key: 56-bits = 72,057,594,037,927,936 keys

Security of 56 Bit DES?

• 29 PCBs of 64 ASICs = 1856 ASICs!

• Checked +90b keys/s 9 days

• Built by EFF in 1998 for $250,000

Advanced Encryption Standard (AES)

• AES Key: 128-bits = 3.402 e+38 = 340,282,366,920,938,463,463,374,607,431,770,000,000

Advanced Encryption Standard (AES)

• AES Key: 128-bits = 3.402 e+38 = 340,282,366,920,938,463,463,374,607,431,770,000,000

• AES Key: 192-bits = 6.277 e+57 = 6,277,101,735,386,680,763,835,789,423,207,700,000,000,000,000,000,000,000,000

Advanced Encryption Standard (AES)

• AES Key: 128-bits = 3.402 e+38 = 340,282,366,920,938,463,463,374,607,431,770,000,000

• AES Key: 192-bits = 6.277 e+57 = 6,277,101,735,386,680,763,835,789,423,207,700,000,000,000,000,000,000,000,000

• AES Key: 256-bits = 1.157 e+77 = 115,792,089,237,316,195,423,570,985,008,690,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000

Measuring Key Quality

EntropyThe likelihood of selecting any single

key out of all possible keys.

How to Measure Entropy?

0x50615373576F5264

How to Measure Entropy?

0x50 61 53 73 57 6F 52 64 P a S s W o R d

How to Measure Entropy?

0x50 61 53 73 57 6F 52 64 P a S s W o R d

• Many keys are derived from passwords.

• Memorizable pwds = negative effect on entropy.

Entropy of Passwords

• 64-bits = 1.8 E+19 = 18,446,744,073,709,551,616 keys

Entropy of Passwords

• 64-bits = 1.8 E+19 = 18,446,744,073,709,551,616 keys

• 8 chars of lower, upper, numeric = 62^8 = 218,340,105,584,896

Entropy of Passwords

• 64-bits = 1.8 E+19 = 18,446,744,073,709,551,616 keys

• 8 chars of lower, upper, numeric = 62^8 = 218,340,105,584,896 ~ 47 bits

Entropy of Passwords

• 64-bits = 1.8 E+19 = 18,446,744,073,709,551,616 keys

• 8 chars of lower, upper, numeric = 62^8 = 218,340,105,584,896 ~ 47 bits

– Deep Crack Brute Force in 40 minutes!

Entropy of Passwords

• 64-bits = 1.8 E+19 = 18,446,744,073,709,551,616 keys

• 8 chars of lower, upper, numeric = 62^8 = 218,340,105,584,896 ~ 47 bits

– Deep Crack Brute Force in 40 minutes!

• 8 chars of alpha-only = 52^8 = 53,459,728,531,456 ~ 45 bits

Entropy of Passwords

• 64-bits = 1.8 E+19 = 18,446,744,073,709,551,616 keys

• 8 chars of lower, upper, numeric = 62^8 = 218,340,105,584,896 ~ 47 bits

– Deep Crack Brute Force in 40 minutes!

• 8 chars of alpha-only = 52^8 = 53,459,728,531,456 ~ 45 bits

• 8 chars, lower-only = 26^8 = 208,827,064,576 ~ 37 bits

Measuring Key Entropy

Dictionary Attacks

• Reduce entropy by leveraging language patterns

Dictionary Attacks

• Reduce entropy by leveraging language patterns

• Merriam-Webster: 250,000 words 250,000 special/scientific 250,000 proper nouns (?) - 1,000 words that are <5 characters= 740,000 ~ 19 bits

Dictionary Attacks

• Reduce entropy by leveraging language patterns

• Merriam-Webster: 250,000 words 250,000 special/scientific 250,000 proper nouns (?) - 1,000 words that are <5 characters= 740,000 ~ 19 bits

• Random use of upper and lower case – Add one bit per char length (max)

• Random use of upper, lower and numbers – Add ~1.5 bits per char length (max)

Cryptographic Hashing

• Works like a CRC or checksum

• Impossible to reverse

• 128, 160 and 256 bits long

• Small changes in the plaintext create vast changes in the hash

• MD5, SHA-1, SHA-256

Hashing Applications

• Validating data– Verifying download packages (md5sum)

• Increasing key entropy– 2n hash operations adds n bits of entropy

• Obscuring passwords

Sending Passwords in the Clear

Obscuring Passwords

“hello”

hash

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

Replay Attack

“hello”

hash

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

Challenge-Response Protocol

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

2151 B9B9 0BD3 FEFA A626 9451 5A44 54F5 9950 ADC6

Challenge

User’s Workstation

2151 B9B9 0BD3 FEFA A626 9451 5A44 54F5 9950 ADC6

Server

Challenge-Response Protocol

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

Response User’s Workstation

2151 B9B9 0BD3 FEFA A626 9451 5A44 54F5 9950 ADC6

Server

“hello”

hash

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

hash

AD58 A056 57C6 C6C5 EFBC 1029 34DB 7F59 7180 8AD4

AD58 A056 57C6 C6C5 EFBC 1029 34DB 7F59 7180 8AD4

2151 B9B9 0BD3 FEFA A626 9451 5A44 54F5 9950 ADC6 hash

Challenge-Response Protocol

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

Response User’s Workstation

2151 B9B9 0BD3 FEFA A626 9451 5A44 54F5 9950 ADC6

Server

“hello”

hash

3401 a6f3 9ee0 82c4 c62b8827 bd6e 9916 0ac3 4a3d

hash

AD58 A056 57C6 C6C5 EFBC 1029 34DB 7F59 7180 8AD4

AD58 A056 57C6 C6C5 EFBC 1029 34DB 7F59 7180 8AD4

2151 B9B9 0BD3 FEFA A626 9451 5A44 54F5 9950 ADC6 hash

NTLM Authentication

“hello”

LM Hash

3401 a6f3 9ee0 82c4 bd6e 9916 0ac3 4a3d

3401 a6f3 9ee0 82 c4 bd6e 9916 0ac3 4a3d

7 bytes 7 bytes 2 bytes

16 bytes

DES

2151 B9B9 0BD3 FEFA

Server Challenge (8 bytes)

DES DES

AD58 A056 57C6 C6C5

Client Response #1 (24 bytes)

8827 bd6e 9916 0ac3 3401 a6f3 9ee0 82c4

“hello”

LM Hash

3401 a6f3 9ee0 82c4 bd6e 9916 0ac3 4a3d

3401 a6f3 9ee0 82 c4 bd6e 9916 0ac3 4a3d

7 bytes 7 bytes 2 bytes

16 bytes

DES

2151 B9B9 0BD3 FEFA

Server Challenge (8 bytes)

DES DES

AD58 A056 57C6 C6C5

Client Response #1 (24 bytes)

8827 bd6e 9916 0ac3 3401 a6f3 9ee0 82c4

!

NTLM Authentication

0000 0000 00

Recommended Reading

• “Applied Cryptography” By Bruce Schneier

• “Practical Cryptography” By Bruce Schneier

• “Secrets and Lies” By Bruce Schneier

• “Cryptographic Security Architecture” By Peter Gutmann

• “Parallelizable Enciphering Mode” By Phillip Rogaway

Organizations• Commercial

– Schneier.com• CryptoGram & blog

– RSA, Inc. (rsa.com)• PKCS

– Internet Engineering Taskforce (ietf.org)• RFCs

– ANSI, ISO, IEEE, W3C

• Government– Natl. Inst. of Standards & Tech.

(nist.gov)• FIPS & SP-800 documents

– Natl. Security Agency (NSA)

Happy Crypting!

Presentation Created By Dave StycosApril, 2010

© 2010, Zocalo Data Systems, Ltd.