MD5 Generator

MD5 (Message-Digest Algorithm 5) is a widely used cryptographic hash function that produces a 128-bit (16-byte) hash value, typically expressed as a 32-digit hexadecimal number. It was designed by Ronald Rivest in 1991 to replace the earlier MD4 algorithm and was specified in RFC 1321 in April 1992.

Despite its security vulnerabilities, MD5 is still commonly used for non-security applications such as checksums to verify data integrity and detect unintentional data corruption. It remains suitable for other non-cryptographic purposes due to its lower computational requirements compared to more recent secure hash algorithms.

MD5 was designed by Professor Ronald Rivest of MIT as a more secure replacement for MD4. The algorithm takes an input message of arbitrary length and produces a 128-bit "fingerprint" or "message digest" as output. The MD5 algorithm is designed to be quite fast on 32-bit machines and doesn't require large substitution tables, allowing for compact implementation.

The algorithm processes a variable-length message into a fixed-length output of 128 bits by breaking the input into 512-bit blocks. It operates on a 128-bit state divided into four 32-bit words (A, B, C, and D) and goes through four rounds of operations, with each round performing 16 operations based on non-linear functions, modular addition, and bit rotation.

// Initialize variables
A = 0x67452301
B = 0xEFCDAB89
C = 0x98BADCFE
D = 0x10325476

// Prepare functions
F(X,Y,Z) = (X AND Y) OR ((NOT X) AND Z)
G(X,Y,Z) = (X AND Z) OR (Y AND (NOT Z))
H(X,Y,Z) = X XOR Y XOR Z
I(X,Y,Z) = Y XOR (X OR (NOT Z))

// Process message (message must be a multiple of 512 bits)
// Pad message until its length ≡ 448 (mod 512)
// Append 64-bit representation of original message length

// Main loop
for each 512-bit chunk of padded message:
    // Break chunk into sixteen 32-bit words (M[0..15])
    // Copy chunk state
    AA = A
    BB = B
    CC = C
    DD = D
    
    // Round 1
    for i from 0 to 15:
        A = B + ((A + F(B,C,D) + M[i] + T[i]) <<< s[i])
        Rotate A, B, C, D
    
    // Round 2
    for i from 16 to 31:
        A = B + ((A + G(B,C,D) + M[(5*i + 1) mod 16] + T[i]) <<< s[i])
        Rotate A, B, C, D
    
    // Round 3
    for i from 32 to 47:
        A = B + ((A + H(B,C,D) + M[(3*i + 5) mod 16] + T[i]) <<< s[i])
        Rotate A, B, C, D
    
    // Round 4
    for i from 48 to 63:
        A = B + ((A + I(B,C,D) + M[(7*i) mod 16] + T[i]) <<< s[i])
        Rotate A, B, C, D
    
    // Add chunk processing result
    A = A + AA
    B = B + BB
    C = C + CC
    D = D + DD

// Output
MD5 = A || B || C || D // Concatenated to 128-bit result

In 1996, a flaw was discovered in the design of MD5, though it wasn't considered fatal at the time. By 2004, more serious vulnerabilities were found, and researchers demonstrated practical collision attacks - methods to create pairs of different inputs that produce the same MD5 hash value.

In 2008, a group of researchers used these vulnerabilities to create a forged SSL certificate that appeared legitimate. The Flame malware exploited MD5 weaknesses to fake a Microsoft digital signature in 2012. Modern collision attacks can find MD5 collisions in seconds on standard computer hardware.