Hashing algorithms

MD5

• Size: 128 bits - 16 bytes - 32 hex

cat file.txt | md5sum
# 930db08d7fb48a7e8a524e736f7acae9

SHA

• SHA1: 160bits
• Applications: git
• SHA256: 256bit
• Complex and time consuming
• Used in applications where you want it to be a expensive operation
• Applications: security and cryptography
• SHA384: 384bit
• SHA512: 512bit

# SHA1 hash
echo -n "Hello" | shasum

# SHA256 hash
echo -n "Hello" | shasum -a 256

# SHA512 hash
echo -n "Hello" | shasum -a 512

• Number of different hashes from SHA1 hash function
• 2^160 = 16^40 = 1.461501637×10^48
• Chance of producing same exact hash for different files in SHA1 (Dice theory)
• Probability of each SHA1 hash: 1/(2^160)
• Probability of same exact hash: (1/(2^160))*(1/_(2^160)) = 1/(2^320)
• Chance of producing any exact hash for different files in SHA1 (Hash collision probability)
• Probability of same any hash: for 2 files: 2.84*10^49
• The probability increases with more files. E.g., 3 files -> 2.05*10^48

HMAC

• Hash with a key: Additional level of security