Pseudo-code for RIPEMD-128

  RIPEMD-128 is an iterative hash function that operates on 32-bit words.
  The round function takes as input a 4-word chaining variable and a 16-word
  message block and maps this to a new chaining variable. All operations are
  defined on 32-bit words. Padding is identical to that of MD4.


  RIPEMD-128: definitions


    nonlinear functions at bit level: exor, mux, -, mux

    f(j, x, y, z) = x XOR y XOR z                (0 <= j <= 15)
    f(j, x, y, z) = (x AND y) OR (NOT(x) AND z)  (16 <= j <= 31)
    f(j, x, y, z) = (x OR NOT(y)) XOR z          (32 <= j <= 47)
    f(j, x, y, z) = (x AND z) OR (y AND NOT(z))  (48 <= j <= 63)


    added constants (hexadecimal)

    K(j) = 0x00000000      (0 <= j <= 15)     
    K(j) = 0x5A827999     (16 <= j <= 31)      int(2**30 x sqrt(2))
    K(j) = 0x6ED9EBA1     (32 <= j <= 47)      int(2**30 x sqrt(3))
    K(j) = 0x8F1BBCDC     (48 <= j <= 63)      int(2**30 x sqrt(5))
    K'(j) = 0x50A28BE6     (0 <= j <= 15)      int(2**30 x cbrt(2))
    K'(j) = 0x5C4DD124    (16 <= j <= 31)      int(2**30 x cbrt(3))
    K'(j) = 0x6D703EF3    (32 <= j <= 47)      int(2**30 x cbrt(5))
    K'(j) = 0x00000000    (48 <= j <= 63)
	    

    selection of message word

    r(j)      = j                    (0 <= j <= 15)
    r(16..31) = 7, 4, 13, 1, 10, 6, 15, 3, 12, 0, 9, 5, 2, 14, 11, 8
    r(32..47) = 3, 10, 14, 4, 9, 15, 8, 1, 2, 7, 0, 6, 13, 11, 5, 12
    r(48..63) = 1, 9, 11, 10, 0, 8, 12, 4, 13, 3, 7, 15, 14, 5, 6, 2
    r'(0..15) = 5, 14, 7, 0, 9, 2, 11, 4, 13, 6, 15, 8, 1, 10, 3, 12
    r'(16..31)= 6, 11, 3, 7, 0, 13, 5, 10, 14, 15, 8, 12, 4, 9, 1, 2
    r'(32..47)= 15, 5, 1, 3, 7, 14, 6, 9, 11, 8, 12, 2, 10, 0, 4, 13
    r'(48..63)= 8, 6, 4, 1, 3, 11, 15, 0, 5, 12, 2, 13, 9, 7, 10, 14


    amount for rotate left (rol)

    s(0..15)  = 11, 14, 15, 12, 5, 8, 7, 9, 11, 13, 14, 15, 6, 7, 9, 8
    s(16..31) = 7, 6, 8, 13, 11, 9, 7, 15, 7, 12, 15, 9, 11, 7, 13, 12
    s(32..47) = 11, 13, 6, 7, 14, 9, 13, 15, 14, 8, 13, 6, 5, 12, 7, 5
    s(48..63) = 11, 12, 14, 15, 14, 15, 9, 8, 9, 14, 5, 6, 8, 6, 5, 12
    s'(0..15) = 8, 9, 9, 11, 13, 15, 15, 5, 7, 7, 8, 11, 14, 14, 12, 6
    s'(16..31)= 9, 13, 15, 7, 12, 8, 9, 11, 7, 7, 12, 7, 6, 15, 13, 11
    s'(32..47)= 9, 7, 15, 11, 8, 6, 6, 14, 12, 13, 5, 14, 13, 13, 7, 5
    s'(48..63)= 15, 5, 8, 11, 14, 14, 6, 14, 6, 9, 12, 9, 12, 5, 15, 8


    initial value (hexadecimal)

    h0 = 0x67452301; h1 = 0xEFCDAB89; h2 = 0x98BADCFE; h3 = 0x10325476; 


  RIPEMD-128: pseudo-code

    It is assumed that the message after padding consists of t 16-word blocks
    that will be denoted with X[i][j], with 0 <= i <= t-1 and 0 <= j <= 15. 
    The symbol [+] denotes addition modulo 2**32 and rol_s denotes cyclic left
    shift (rotate) over s positions. 


    for i := 0 to t-1 {
        A := h0; B := h1; C := h2; D = h3;
        A' := h0; B' := h1; C' := h2; D' = h3;
        for j := 0 to 63 {
            T := rol_s(j)(A [+] f(j, B, C, D) [+] X[i][r(j)] [+] K(j));
            A := D; D := C; C := B; B := T;
            T := rol_s'(j)(A' [+] f(63-j, B', C', D') [+] X[i][r'(j)] [+] K'(j));
            A' := D'; D' := C'; C' := B'; B' := T;
        }
        T := h1 [+] C [+] D'; h1 := h2 [+] D [+] A'; h2 := h3 [+] A [+] B';
        h3 := h0 [+] B [+] C'; h0 := T;
    }