Security and Cryptography in Python

Security and Cryptography in Python - Hash Functions(1)

Properties of a Hash Function

1. It is an one-way deterministic function
2. The output is dependent on all input bits
3. Output is uniformly distributed
4. "Impossible" (difficult) make a collision

Use of Hash Functions

1. Digital signature
2. Shadow files (passwords)
3. HMAC
4. Make deterministic identifiers

Code in Python:

import hashlib

def modify(m):
    l = list(m)
    l[0] = l[0] ^ 1
    return bytes(l)

m = "This is the hash value message".encode()

sha256 = hashlib.sha256()
sha256.update(m)
d = sha256.digest()
print(d)

sha256 = hashlib.sha256()
sha256.update(m)
d = sha256.digest()
print(d)

m = modify(m)
print(m)

sha256 = hashlib.sha256()
sha256.update(m)
d = sha256.digest()
print(d)

Running Result: