1 /* R_DH.C - Diffie-Hellman routines for RSAREF
4 /* Copyright (C) RSA Laboratories, a division of RSA Data Security,
5 Inc., created 1993. All rights reserved.
14 /* Generates Diffie-Hellman parameters.
16 int R_GenerateDHParams (params, primeBits, subPrimeBits, randomStruct)
17 R_DH_PARAMS *params; /* new Diffie-Hellman parameters */
18 unsigned int primeBits; /* length of prime in bits */
19 unsigned int subPrimeBits; /* length of subprime in bits */
20 R_RANDOM_STRUCT *randomStruct; /* random structure */
23 NN_DIGIT g[MAX_NN_DIGITS], p[MAX_NN_DIGITS], q[MAX_NN_DIGITS],
24 t[MAX_NN_DIGITS], u[MAX_NN_DIGITS], v[MAX_NN_DIGITS];
27 pDigits = (primeBits + NN_DIGIT_BITS - 1) / NN_DIGIT_BITS;
29 /* Generate subprime q between 2^(subPrimeBits-1) and
30 2^subPrimeBits-1, searching in steps of 2.
32 NN_Assign2Exp (t, subPrimeBits-1, pDigits);
33 NN_Assign (u, t, pDigits);
34 NN_ASSIGN_DIGIT (v, 1, pDigits);
35 NN_Sub (v, t, v, pDigits);
36 NN_Add (u, u, v, pDigits);
37 NN_ASSIGN_DIGIT (v, 2, pDigits);
38 if (status = GeneratePrime (q, t, u, v, pDigits, randomStruct))
41 /* Generate prime p between 2^(primeBits-1) and 2^primeBits-1,
42 searching in steps of 2*q.
44 NN_Assign2Exp (t, primeBits-1, pDigits);
45 NN_Assign (u, t, pDigits);
46 NN_ASSIGN_DIGIT (v, 1, pDigits);
47 NN_Sub (v, t, v, pDigits);
48 NN_Add (u, u, v, pDigits);
49 NN_LShift (v, q, 1, pDigits);
50 if (status = GeneratePrime (p, t, u, v, pDigits, randomStruct))
53 /* Generate generator g for subgroup as 2^((p-1)/q) mod p.
55 NN_ASSIGN_DIGIT (g, 2, pDigits);
56 NN_Div (t, u, p, pDigits, q, pDigits);
57 NN_ModExp (g, g, t, pDigits, p, pDigits);
59 params->generatorLen = params->primeLen = DH_PRIME_LEN (primeBits);
60 NN_Encode (params->prime, params->primeLen, p, pDigits);
61 NN_Encode (params->generator, params->generatorLen, g, pDigits);
66 /* Sets up Diffie-Hellman key agreement. Public value has same length
69 int R_SetupDHAgreement
70 (publicValue, privateValue, privateValueLen, params, randomStruct)
71 unsigned char *publicValue; /* new public value */
72 unsigned char *privateValue; /* new private value */
73 unsigned int privateValueLen; /* length of private value */
74 R_DH_PARAMS *params; /* Diffie-Hellman parameters */
75 R_RANDOM_STRUCT *randomStruct; /* random structure */
78 NN_DIGIT g[MAX_NN_DIGITS], p[MAX_NN_DIGITS], x[MAX_NN_DIGITS],
80 unsigned int pDigits, xDigits;
82 NN_Decode (p, MAX_NN_DIGITS, params->prime, params->primeLen);
83 pDigits = NN_Digits (p, MAX_NN_DIGITS);
84 NN_Decode (g, pDigits, params->generator, params->generatorLen);
86 /* Generate private value.
88 if (status = R_GenerateBytes (privateValue, privateValueLen, randomStruct))
90 NN_Decode (x, pDigits, privateValue, privateValueLen);
91 xDigits = NN_Digits (x, pDigits);
93 /* Compute y = g^x mod p.
95 NN_ModExp (y, g, x, xDigits, p, pDigits);
97 NN_Encode (publicValue, params->primeLen, y, pDigits);
99 /* Zeroize sensitive information.
101 R_memset ((POINTER)x, 0, sizeof (x));
106 /* Computes agreed key from the other party's public value, a private
107 value, and Diffie-Hellman parameters. Other public value and
108 agreed-upon key have same length as prime.
110 Requires otherPublicValue < prime.
112 int R_ComputeDHAgreedKey
113 (agreedKey, otherPublicValue, privateValue, privateValueLen, params)
114 unsigned char *agreedKey; /* new agreed key */
115 unsigned char *otherPublicValue; /* other's public value */
116 unsigned char *privateValue; /* private value */
117 unsigned int privateValueLen; /* length of private value */
118 R_DH_PARAMS *params; /* Diffie-Hellman parameters */
120 NN_DIGIT p[MAX_NN_DIGITS], x[MAX_NN_DIGITS], y[MAX_NN_DIGITS],
122 unsigned int pDigits, xDigits;
124 NN_Decode (p, MAX_NN_DIGITS, params->prime, params->primeLen);
125 pDigits = NN_Digits (p, MAX_NN_DIGITS);
126 NN_Decode (x, pDigits, privateValue, privateValueLen);
127 xDigits = NN_Digits (x, pDigits);
128 NN_Decode (y, pDigits, otherPublicValue, params->primeLen);
130 if (NN_Cmp (y, p, pDigits) >= 0)
133 /* Compute z = y^x mod p.
135 NN_ModExp (z, y, x, xDigits, p, pDigits);
137 NN_Encode (agreedKey, params->primeLen, z, pDigits);
139 /* Zeroize sensitive information.
141 R_memset ((POINTER)x, 0, sizeof (x));
142 R_memset ((POINTER)z, 0, sizeof (z));