sec/Security/SecDH.c

   1 /*
   2  * Copyright (c) 2007-2008,2010 Apple Inc. All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 /*
  25  * SecDH.c - Implement the crypto required for a Diffie-Hellman key exchange.
  26  */
  27
  28 #include "SecDH.h"
  29 #include <libDER/DER_Keys.h>
  30 #include <corecrypto/ccdh.h>
  31 #include <libDER/DER_Keys.h>
  32 #include <libDER/DER_Encode.h>
  33 #include <libDER/asn1Types.h>
  34 #include <libkern/OSByteOrder.h>
  35 #include <security_utilities/debugging.h>
  36 #include <Security/SecInternal.h>
  37 #include <Security/SecRandom.h>
  38 #include <stdlib.h>
  39 #include <MacErrors.h>
  40 #include <Security/SecBasePriv.h>
  41
  42 #ifdef DEBUG
  43 #define DH_DEBUG  1
  44 #endif
  45
  46 static inline ccdh_gp_t SecDH_gp(SecDHContext dh)
  47 {
  48     void *p = dh;
  49     ccdh_gp_t gp = { .gp = p };
  50     return gp;
  51 }
  52
  53 static inline ccdh_full_ctx_t SecDH_priv(SecDHContext dh)
  54 {
  55     void *p = dh;
  56     cczp_t zp = { .u = p };
  57     cc_size s = ccn_sizeof_n(cczp_n(zp));
  58     ccdh_full_ctx_t priv = { .hdr = (struct ccdh_ctx_header *)(p+ccdh_gp_size(s)) };
  59     return priv;
  60 }
  61
  62 static inline size_t SecDH_context_size(size_t p_len)
  63 {
  64     cc_size n = ccn_nof_size(p_len);
  65     cc_size real_p_len = ccn_sizeof_n(n);
  66     size_t context_size = ccdh_gp_size(real_p_len)+ccdh_full_ctx_size(real_p_len);
  67     return context_size;
  68 }
  69
  70 /* Shared static functions. */
  71
  72 static OSStatus
  73 der2OSStatus(DERReturn derReturn)
  74 {
  75         switch(derReturn)
  76         {
  77         case DR_Success:                                return noErr;
  78         case DR_EndOfSequence:                  return errSecDecode;
  79         case DR_UnexpectedTag:                  return errSecDecode;
  80         case DR_DecodeError:                    return errSecDecode;
  81         case DR_Unimplemented:                  return unimpErr;
  82         case DR_IncompleteSeq:                  return errSecDecode;
  83         case DR_ParamErr:                               return paramErr;
  84         case DR_BufOverflow:                    return errSecBufferTooSmall;
  85         default:                                                return errSecInternal;
  86         }
  87 }
  88
  89 static int dhRngCallback(struct ccrng_state *rng, unsigned long outlen, void *out)
  90 {
  91     return SecRandomCopyBytes(kSecRandomDefault, outlen, out);
  92 }
  93
  94 static struct ccrng_state dhrng = {
  95     .generate = dhRngCallback
  96 };
  97
  98 OSStatus SecDHCreate(uint32_t g, const uint8_t *p, size_t p_len,
  99         uint32_t l, const uint8_t *recip, size_t recip_len, SecDHContext *pdh)
 100 {
 101     cc_size n = ccn_nof_size(p_len);
 102     size_t context_size = SecDH_context_size(p_len);
 103     void *context = malloc(context_size);
 104     bzero(context, context_size);
 105
 106     ccdh_gp_t gp;
 107     gp.gp = context;
 108
 109     CCDH_GP_N(gp) = n;
 110     CCDH_GP_L(gp) = l;
 111
 112     if(ccn_read_uint(n, CCDH_GP_PRIME(gp), p_len, p))
 113         goto errOut;
 114     if(recip) {
 115         if(ccn_read_uint(n+1, CCDH_GP_RECIP(gp), recip_len, recip))
 116             goto errOut;
 117         gp.zp.zp->mod_prime = cczp_mod;
 118     } else {
 119         cczp_init(gp.zp);
 120     };
 121     ccn_seti(n, CCDH_GP_G(gp), g);
 122
 123     *pdh = (SecDHContext) context;
 124
 125     return noErr;
 126
 127 errOut:
 128     SecDHDestroy(context);
 129     *pdh = NULL;
 130     return errSecInternal;
 131
 132 }
 133
 134 /* this used to be in libgDH */
 135 /*
 136  * Support for encoding and decoding DH parameter blocks.
 137  * Apple form encodes the reciprocal of the prime p.
 138  */
 139 /* PKCS3, Openssl compatible */
 140 typedef struct {
 141         DERItem                         p;
 142         DERItem                         g;
 143         DERItem                         l;
 144         DERItem                         recip; /* Only used in Apple Custom blocks. */
 145 } DER_DHParams;
 146
 147 static const DERItemSpec DER_DHParamsItemSpecs[] =
 148 {
 149         { DER_OFFSET(DER_DHParams, p),
 150         ASN1_INTEGER,
 151         DER_DEC_NO_OPTS | DER_ENC_SIGNED_INT },
 152         { DER_OFFSET(DER_DHParams, g),
 153         ASN1_INTEGER,
 154         DER_DEC_NO_OPTS | DER_ENC_SIGNED_INT },
 155         { DER_OFFSET(DER_DHParams, l),
 156         ASN1_INTEGER,
 157         DER_DEC_OPTIONAL | DER_ENC_SIGNED_INT },
 158     /* Not part of PKCS3 per-se, but we add it on just for kicks.  Since
 159      it's optional we will automatically decode any apple specific
 160      params, but we won't add this section unless the caller asks
 161      us to.  */
 162         { DER_OFFSET(DER_DHParams, recip),
 163         ASN1_PRIVATE | ASN1_PRIMITIVE | 0,
 164         DER_DEC_OPTIONAL | DER_ENC_SIGNED_INT },
 165 };
 166 static const DERSize DER_NumDHParamsItemSpecs =
 167 sizeof(DER_DHParamsItemSpecs) / sizeof(DERItemSpec);
 168
 169
 170 OSStatus SecDHCreateFromParameters(const uint8_t *params,
 171         size_t params_len, SecDHContext *pdh)
 172 {
 173     DERReturn drtn;
 174         DERItem paramItem = {(DERByte *)params, params_len};
 175         DER_DHParams decodedParams;
 176     uint32_t l;
 177
 178     drtn = DERParseSequence(&paramItem,
 179                             DER_NumDHParamsItemSpecs, DER_DHParamsItemSpecs,
 180                             &decodedParams, sizeof(decodedParams));
 181     if(drtn)
 182         return drtn;
 183
 184     drtn = DERParseInteger(&decodedParams.l, &l);
 185     if(drtn)
 186         return drtn;
 187     cc_size n = ccn_nof_size(decodedParams.p.length);
 188     cc_size p_len = ccn_sizeof_n(n);
 189     size_t context_size = ccdh_gp_size(p_len)+ccdh_full_ctx_size(p_len);
 190     void *context = malloc(context_size);
 191     if(context==NULL)
 192         return memFullErr;
 193
 194     bzero(context, context_size);
 195
 196     ccdh_gp_t gp;
 197     gp.gp = context;
 198
 199     CCDH_GP_N(gp) = n;
 200     CCDH_GP_L(gp) = l;
 201
 202     if(ccn_read_uint(n, CCDH_GP_PRIME(gp), decodedParams.p.length, decodedParams.p.data))
 203         goto errOut;
 204     if(decodedParams.recip.length) {
 205         if(ccn_read_uint(n+1, CCDH_GP_RECIP(gp), decodedParams.recip.length, decodedParams.recip.data))
 206             goto errOut;
 207         gp.zp.zp->mod_prime = cczp_mod;
 208     } else {
 209         cczp_init(gp.zp);
 210     };
 211
 212     if(ccn_read_uint(n, CCDH_GP_G(gp), decodedParams.g.length, decodedParams.g.data))
 213         goto errOut;
 214
 215     *pdh = (SecDHContext) context;
 216     return noErr;
 217
 218 errOut:
 219     SecDHDestroy(context);
 220     *pdh = NULL;
 221     return errSecInvalidKey;
 222 }
 223
 224 OSStatus SecDHCreateFromAlgorithmId(const uint8_t *alg, size_t alg_len,
 225         SecDHContext *pdh) {
 226         DERAlgorithmId algorithmId;
 227         DERItem algId;
 228
 229         algId.data = (uint8_t *)alg;
 230         algId.length = alg_len;
 231
 232         DERReturn drtn = DERParseSequence(&algId,
 233                 DERNumAlgorithmIdItemSpecs, DERAlgorithmIdItemSpecs,
 234                 &algorithmId, sizeof(algorithmId));
 235         if (drtn != DR_Success)
 236                 return der2OSStatus(drtn);
 237
 238     return SecDHCreateFromParameters(algorithmId.params.data,
 239                 algorithmId.params.length, pdh);
 240 }
 241
 242 size_t SecDHGetMaxKeyLength(SecDHContext dh) {
 243     cczp_const_t zp;
 244     zp.u = (cc_unit *)dh;
 245
 246     return ccn_sizeof_n(cczp_n(zp));
 247 }
 248
 249
 250 OSStatus SecDHGenerateKeypair(SecDHContext dh, uint8_t *pub_key,
 251         size_t *pub_key_len)
 252 {
 253     int result;
 254     ccdh_gp_t gp = SecDH_gp(dh);
 255     ccdh_full_ctx_t priv = SecDH_priv(dh);
 256
 257     if((result = ccdh_generate_key(gp, &dhrng, priv)))
 258         return result;
 259
 260     /* output y as a big endian byte buffer */
 261     size_t ylen = ccn_write_uint_size(ccdh_gp_n(gp), ccdh_ctx_y(priv));
 262     if(*pub_key_len < ylen)
 263        return errSecBufferTooSmall;
 264     ccn_write_uint(ccdh_gp_n(gp),ccdh_ctx_y(priv), ylen, pub_key);
 265     *pub_key_len = ylen;
 266
 267     return noErr;
 268 }
 269
 270 OSStatus SecDHComputeKey(SecDHContext dh,
 271         const uint8_t *pub_key, size_t pub_key_len,
 272     uint8_t *computed_key, size_t *computed_key_len)
 273 {
 274     ccdh_gp_t gp = SecDH_gp(dh);
 275     ccdh_full_ctx_t priv = SecDH_priv(dh);
 276     ccdh_pub_ctx_decl_gp(gp, pub);
 277     cc_size n = ccdh_gp_n(gp);
 278     cc_unit r[n];
 279
 280     if(ccdh_import_pub(gp, pub_key_len, pub_key, pub))
 281         return errSecInvalidKey;
 282
 283     if(ccdh_compute_key(priv, pub, r))
 284         return errSecInvalidKey;
 285
 286     ccn_write_uint(n, r, *computed_key_len, computed_key);
 287     size_t out_size = ccn_write_uint_size(n, r);
 288     if(out_size < *computed_key_len)
 289         *computed_key_len=out_size;
 290
 291     return noErr;
 292 }
 293
 294 void SecDHDestroy(SecDHContext dh) {
 295         /* Zero out key material. */
 296     ccdh_gp_t gp = SecDH_gp(dh);
 297     cc_size p_len = ccn_sizeof_n(ccdh_gp_n(gp));
 298     size_t context_size = SecDH_context_size(p_len);
 299
 300     bzero(dh, context_size);
 301     free(dh);
 302 }