doc/crypto/ecdsa.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 ecdsa - Elliptic Curve Digital Signature Algorithm
   6
   7 =head1 SYNOPSIS
   8
   9  #include <openssl/ecdsa.h>
  10
  11  ECDSA_SIG*     ECDSA_SIG_new(void);
  12  void           ECDSA_SIG_free(ECDSA_SIG *sig);
  13  int            i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp);
  14  ECDSA_SIG*     d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp,
  15                 long len);
  16
  17  ECDSA_SIG*     ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
  18                         EC_KEY *eckey);
  19  ECDSA_SIG*     ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,
  20                         const BIGNUM *kinv, const BIGNUM *rp,
  21                         EC_KEY *eckey);
  22  int            ECDSA_do_verify(const unsigned char *dgst, int dgst_len,
  23                         const ECDSA_SIG *sig, EC_KEY* eckey);
  24  int            ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx,
  25                         BIGNUM **kinv, BIGNUM **rp);
  26  int            ECDSA_sign(int type, const unsigned char *dgst,
  27                         int dgstlen, unsigned char *sig,
  28                         unsigned int *siglen, EC_KEY *eckey);
  29  int            ECDSA_sign_ex(int type, const unsigned char *dgst,
  30                         int dgstlen, unsigned char *sig,
  31                         unsigned int *siglen, const BIGNUM *kinv,
  32                         const BIGNUM *rp, EC_KEY *eckey);
  33  int            ECDSA_verify(int type, const unsigned char *dgst,
  34                         int dgstlen, const unsigned char *sig,
  35                         int siglen, EC_KEY *eckey);
  36  int            ECDSA_size(const EC_KEY *eckey);
  37
  38  const ECDSA_METHOD*    ECDSA_OpenSSL(void);
  39  void           ECDSA_set_default_method(const ECDSA_METHOD *meth);
  40  const ECDSA_METHOD*    ECDSA_get_default_method(void);
  41  int            ECDSA_set_method(EC_KEY *eckey,const ECDSA_METHOD *meth);
  42
  43  int            ECDSA_get_ex_new_index(long argl, void *argp,
  44                         CRYPTO_EX_new *new_func,
  45                         CRYPTO_EX_dup *dup_func,
  46                         CRYPTO_EX_free *free_func);
  47  int            ECDSA_set_ex_data(EC_KEY *d, int idx, void *arg);
  48  void*          ECDSA_get_ex_data(EC_KEY *d, int idx);
  49
  50 =head1 DESCRIPTION
  51
  52 The B<ECDSA_SIG> structure consists of two BIGNUMs for the
  53 r and s value of a ECDSA signature (see X9.62 or FIPS 186-2).
  54
  55  struct
  56         {
  57         BIGNUM *r;
  58         BIGNUM *s;
  59  } ECDSA_SIG;
  60
  61 ECDSA_SIG_new() allocates a new B<ECDSA_SIG> structure (note: this
  62 function also allocates the BIGNUMs) and initialize it.
  63
  64 ECDSA_SIG_free() frees the B<ECDSA_SIG> structure B<sig>.
  65
  66 i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature
  67 B<sig> and writes the encoded signature to B<*pp> (note: if B<pp>
  68 is NULL B<i2d_ECDSA_SIG> returns the expected length in bytes of
  69 the DER encoded signature). B<i2d_ECDSA_SIG> returns the length
  70 of the DER encoded signature (or 0 on error).
  71
  72 d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns
  73 the decoded signature in a newly allocated B<ECDSA_SIG> structure.
  74 B<*sig> points to the buffer containing the DER encoded signature
  75 of size B<len>.
  76
  77 ECDSA_size() returns the maximum length of a DER encoded
  78 ECDSA signature created with the private EC key B<eckey>.
  79
  80 ECDSA_sign_setup() may be used to precompute parts of the
  81 signing operation. B<eckey> is the private EC key and B<ctx>
  82 is a pointer to B<BN_CTX> structure (or NULL). The precomputed
  83 values or returned in B<kinv> and B<rp> and can be used in a
  84 later call to B<ECDSA_sign_ex> or B<ECDSA_do_sign_ex>.
  85
  86 ECDSA_sign() is wrapper function for ECDSA_sign_ex with B<kinv>
  87 and B<rp> set to NULL.
  88
  89 ECDSA_sign_ex() computes a digital signature of the B<dgstlen> bytes
  90 hash value B<dgst> using the private EC key B<eckey> and the optional
  91 pre-computed values B<kinv> and B<rp>. The DER encoded signatures is
  92 stored in B<sig> and it's length is returned in B<sig_len>. Note: B<sig>
  93 must point to B<ECDSA_size> bytes of memory. The parameter B<type>
  94 is ignored.
  95
  96 ECDSA_verify() verifies that the signature in B<sig> of size
  97 B<siglen> is a valid ECDSA signature of the hash value
  98 value B<dgst> of size B<dgstlen> using the public key B<eckey>.
  99 The parameter B<type> is ignored.
 100
 101 ECDSA_do_sign() is wrapper function for ECDSA_do_sign_ex with B<kinv>
 102 and B<rp> set to NULL.
 103
 104 ECDSA_do_sign_ex() computes a digital signature of the B<dgst_len>
 105 bytes hash value B<dgst> using the private key B<eckey> and the
 106 optional pre-computed values B<kinv> and B<rp>. The signature is
 107 returned in a newly allocated B<ECDSA_SIG> structure (or NULL on error).
 108
 109 ECDSA_do_verify() verifies that the signature B<sig> is a valid
 110 ECDSA signature of the hash value B<dgst> of size B<dgst_len>
 111 using the public key B<eckey>.
 112
 113 =head1 RETURN VALUES
 114
 115 ECDSA_size() returns the maximum length signature or 0 on error.
 116
 117 ECDSA_sign_setup() and ECDSA_sign() return 1 if successful or 0
 118 on error.
 119
 120 ECDSA_verify() and ECDSA_do_verify() return 1 for a valid
 121 signature, 0 for an invalid signature and -1 on error.
 122 The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
 123
 124 =head1 EXAMPLES
 125
 126 Creating a ECDSA signature of given SHA-1 hash value using the
 127 named curve secp192k1.
 128
 129 First step: create a EC_KEY object (note: this part is B<not> ECDSA
 130 specific)
 131
 132  int        ret;
 133  ECDSA_SIG *sig;
 134  EC_KEY    *eckey = EC_KEY_new();
 135  if (eckey == NULL)
 136         {
 137         /* error */
 138         }
 139  key->group = EC_GROUP_new_by_nid(NID_secp192k1);
 140  if (key->group == NULL)
 141         {
 142         /* error */
 143         }
 144  if (!EC_KEY_generate_key(eckey))
 145         {
 146         /* error */
 147         }
 148
 149 Second step: compute the ECDSA signature of a SHA-1 hash value
 150 using B<ECDSA_do_sign>
 151
 152  sig = ECDSA_do_sign(digest, 20, eckey);
 153  if (sig == NULL)
 154         {
 155         /* error */
 156         }
 157
 158 or using B<ECDSA_sign>
 159
 160  unsigned char *buffer, *pp;
 161  int            buf_len;
 162  buf_len = ECDSA_size(eckey);
 163  buffer  = OPENSSL_malloc(buf_len);
 164  pp = buffer;
 165  if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey);
 166         {
 167         /* error */
 168         }
 169
 170 Third step: verify the created ECDSA signature using B<ECDSA_do_verify>
 171
 172  ret = ECDSA_do_verify(digest, 20, sig, eckey);
 173
 174 or using B<ECDSA_verify>
 175
 176  ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);
 177
 178 and finally evaluate the return value:
 179
 180  if (ret == -1)
 181         {
 182         /* error */
 183         }
 184  else if (ret == 0)
 185         {
 186         /* incorrect signature */
 187         }
 188  else   /* ret == 1 */
 189         {
 190         /* signature ok */
 191         }
 192
 193 =head1 CONFORMING TO
 194
 195 ANSI X9.62, US Federal Information Processing Standard FIPS 186-2
 196 (Digital Signature Standard, DSS)
 197
 198 =head1 SEE ALSO
 199
 200 L<dsa(3)|dsa(3)>, L<rsa(3)|rsa(3)>
 201
 202 =head1 HISTORY
 203
 204 The ecdsa implementation was first introduced in OpenSSL 0.9.8
 205
 206 =head1 AUTHOR
 207
 208 Nils Larsch for the OpenSSL project (http://www.openssl.org).
 209
 210 =cut