/* R_DH.C - Diffie-Hellman routines for RSAREF
 */

/* Copyright (C) RSA Laboratories, a division of RSA Data Security,
     Inc., created 1993. All rights reserved.
 */

#include "global.h"
#include "rsaref.h"
#include "r_random.h"
#include "nn.h"
#include "prime.h"

/* Generates Diffie-Hellman parameters.
 */
int R_GenerateDHParams (params, primeBits, subPrimeBits, randomStruct)
R_DH_PARAMS *params;                       /* new Diffie-Hellman parameters */
unsigned int primeBits;                          /* length of prime in bits */
unsigned int subPrimeBits;                    /* length of subprime in bits */
R_RANDOM_STRUCT *randomStruct;                          /* random structure */
{
  int status;
  NN_DIGIT g[MAX_NN_DIGITS], p[MAX_NN_DIGITS], q[MAX_NN_DIGITS],
    t[MAX_NN_DIGITS], u[MAX_NN_DIGITS], v[MAX_NN_DIGITS];
  unsigned int pDigits;

  pDigits = (primeBits + NN_DIGIT_BITS - 1) / NN_DIGIT_BITS;
  
  /* Generate subprime q between 2^(subPrimeBits-1) and
       2^subPrimeBits-1, searching in steps of 2.
   */
  NN_Assign2Exp (t, subPrimeBits-1, pDigits);
  NN_Assign (u, t, pDigits);
  NN_ASSIGN_DIGIT (v, 1, pDigits);
  NN_Sub (v, t, v, pDigits);
  NN_Add (u, u, v, pDigits);
  NN_ASSIGN_DIGIT (v, 2, pDigits);
  if (status = GeneratePrime (q, t, u, v, pDigits, randomStruct))
    return (status);
  
  /* Generate prime p between 2^(primeBits-1) and 2^primeBits-1,
       searching in steps of 2*q.
   */
  NN_Assign2Exp (t, primeBits-1, pDigits);
  NN_Assign (u, t, pDigits);
  NN_ASSIGN_DIGIT (v, 1, pDigits);
  NN_Sub (v, t, v, pDigits);
  NN_Add (u, u, v, pDigits);
  NN_LShift (v, q, 1, pDigits);
  if (status = GeneratePrime (p, t, u, v, pDigits, randomStruct))
    return (status);
  
  /* Generate generator g for subgroup as 2^((p-1)/q) mod p.
   */
  NN_ASSIGN_DIGIT (g, 2, pDigits);
  NN_Div (t, u, p, pDigits, q, pDigits);
  NN_ModExp (g, g, t, pDigits, p, pDigits);

  params->generatorLen = params->primeLen = DH_PRIME_LEN (primeBits);
  NN_Encode (params->prime, params->primeLen, p, pDigits);
  NN_Encode (params->generator, params->generatorLen, g, pDigits);

  return (0);
}

/* Sets up Diffie-Hellman key agreement. Public value has same length
   as prime.
 */
int R_SetupDHAgreement
  (publicValue, privateValue, privateValueLen, params, randomStruct)
unsigned char *publicValue;                             /* new public value */
unsigned char *privateValue;                           /* new private value */
unsigned int privateValueLen;                    /* length of private value */
R_DH_PARAMS *params;                           /* Diffie-Hellman parameters */
R_RANDOM_STRUCT *randomStruct;                          /* random structure */
{
  int status;
  NN_DIGIT g[MAX_NN_DIGITS], p[MAX_NN_DIGITS], x[MAX_NN_DIGITS],
    y[MAX_NN_DIGITS];
  unsigned int pDigits, xDigits;

  NN_Decode (p, MAX_NN_DIGITS, params->prime, params->primeLen);
  pDigits = NN_Digits (p, MAX_NN_DIGITS);
  NN_Decode (g, pDigits, params->generator, params->generatorLen);

  /* Generate private value.
   */
  if (status = R_GenerateBytes (privateValue, privateValueLen, randomStruct))
    return (status);
  NN_Decode (x, pDigits, privateValue, privateValueLen);
  xDigits = NN_Digits (x, pDigits);
  
  /* Compute y = g^x mod p.
   */
  NN_ModExp (y, g, x, xDigits, p, pDigits);

  NN_Encode (publicValue, params->primeLen, y, pDigits);
  
  /* Zeroize sensitive information.
   */
  R_memset ((POINTER)x, 0, sizeof (x));

  return (0);
}

/* Computes agreed key from the other party's public value, a private
   value, and Diffie-Hellman parameters. Other public value and
   agreed-upon key have same length as prime.

   Requires otherPublicValue < prime.
 */
int R_ComputeDHAgreedKey
  (agreedKey, otherPublicValue, privateValue, privateValueLen, params)
unsigned char *agreedKey;                                 /* new agreed key */
unsigned char *otherPublicValue;                    /* other's public value */
unsigned char *privateValue;                               /* private value */
unsigned int privateValueLen;                    /* length of private value */
R_DH_PARAMS *params;                           /* Diffie-Hellman parameters */
{
  NN_DIGIT p[MAX_NN_DIGITS], x[MAX_NN_DIGITS], y[MAX_NN_DIGITS],
    z[MAX_NN_DIGITS];
  unsigned int pDigits, xDigits;

  NN_Decode (p, MAX_NN_DIGITS, params->prime, params->primeLen);
  pDigits = NN_Digits (p, MAX_NN_DIGITS);
  NN_Decode (x, pDigits, privateValue, privateValueLen);
  xDigits = NN_Digits (x, pDigits);
  NN_Decode (y, pDigits, otherPublicValue, params->primeLen);

  if (NN_Cmp (y, p, pDigits) >= 0)
    return (RE_DATA);
  
  /* Compute z = y^x mod p.
   */
  NN_ModExp (z, y, x, xDigits, p, pDigits);

  NN_Encode (agreedKey, params->primeLen, z, pDigits);
  
  /* Zeroize sensitive information.
   */
  R_memset ((POINTER)x, 0, sizeof (x));
  R_memset ((POINTER)z, 0, sizeof (z));

  return (0);
}