™.. ecdsa - Online Linux Manual PageSection : 3
Updated : 2013-02-11
Source : 1.0.1e
Note : OpenSSL
NAMEecdsa − Elliptic Curve Digital Signature Algorithm
SYNOPSIS​ #include <openssl/ecdsa.h> ​ ​ ECDSA_SIG* ECDSA_SIG_new(void); ​ void ECDSA_SIG_free(ECDSA_SIG *sig); ​ int i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp); ​ ECDSA_SIG* d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp, ​ long len); ​ ​ ECDSA_SIG* ECDSA_do_sign(const unsigned char *dgst, int dgst_len, ​ EC_KEY *eckey); ​ ECDSA_SIG* ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen, ​ const BIGNUM *kinv, const BIGNUM *rp, ​ EC_KEY *eckey); ​ int ECDSA_do_verify(const unsigned char *dgst, int dgst_len, ​ const ECDSA_SIG *sig, EC_KEY* eckey); ​ int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx, ​ BIGNUM **kinv, BIGNUM **rp); ​ int ECDSA_sign(int type, const unsigned char *dgst, ​ int dgstlen, unsigned char *sig, ​ unsigned int *siglen, EC_KEY *eckey); ​ int ECDSA_sign_ex(int type, const unsigned char *dgst, ​ int dgstlen, unsigned char *sig, ​ unsigned int *siglen, const BIGNUM *kinv, ​ const BIGNUM *rp, EC_KEY *eckey); ​ int ECDSA_verify(int type, const unsigned char *dgst, ​ int dgstlen, const unsigned char *sig, ​ int siglen, EC_KEY *eckey); ​ int ECDSA_size(const EC_KEY *eckey); ​ ​ const ECDSA_METHOD* ECDSA_OpenSSL(void); ​ void ECDSA_set_default_method(const ECDSA_METHOD *meth); ​ const ECDSA_METHOD* ECDSA_get_default_method(void); ​ int ECDSA_set_method(EC_KEY *eckey,const ECDSA_METHOD *meth); ​ ​ int ECDSA_get_ex_new_index(long argl, void *argp, ​ CRYPTO_EX_new *new_func, ​ CRYPTO_EX_dup *dup_func, ​ CRYPTO_EX_free *free_func); ​ int ECDSA_set_ex_data(EC_KEY *d, int idx, void *arg); ​ void* ECDSA_get_ex_data(EC_KEY *d, int idx);
DESCRIPTIONThe ECDSA_SIG structure consists of two BIGNUMs for the r and s value of a ECDSA signature (see X9.62 or FIPS 186−2). ​ struct ​ { ​ BIGNUM *r; ​ BIGNUM *s; ​ } ECDSA_SIG; ​ECDSA_SIG_new() allocates a new ECDSA_SIG structure (note: this function also allocates the BIGNUMs) and initialize it. ​ECDSA_SIG_free() frees the ECDSA_SIG structure sig. ​i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature ​sig and writes the encoded signature to *pp (note: if pp is NULL i2d_ECDSA_SIG returns the expected length in bytes of the DER encoded signature). i2d_ECDSA_SIG returns the length of the DER encoded signature (or 0 on error). ​d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns the decoded signature in a newly allocated ECDSA_SIG structure. ​*sig points to the buffer containing the DER encoded signature of size len. ​ECDSA_size() returns the maximum length of a DER encoded ​ECDSA signature created with the private EC key eckey. ​ECDSA_sign_setup() may be used to precompute parts of the signing operation. eckey is the private EC key and ctx is a pointer to BN_CTX structure (or NULL). The precomputed values or returned in kinv and rp and can be used in a later call to ECDSA_sign_ex or ECDSA_do_sign_ex. ​ECDSA_sign() is wrapper function for ECDSA_sign_ex with kinv and rp set to NULL. ​ECDSA_sign_ex() computes a digital signature of the dgstlen bytes hash value dgst using the private EC key eckey and the optional pre-computed values kinv and rp. The DER encoded signatures is stored in sig and it's length is returned in sig_len. Note: sig must point to ECDSA_size bytes of memory. The parameter type is ignored. ​ECDSA_verify() verifies that the signature in sig of size ​siglen is a valid ECDSA signature of the hash value value dgst of size dgstlen using the public key eckey. The parameter type is ignored. ​ECDSA_do_sign() is wrapper function for ECDSA_do_sign_ex with kinv and rp set to NULL. ​ECDSA_do_sign_ex() computes a digital signature of the dgst_len bytes hash value dgst using the private key eckey and the optional pre-computed values kinv and rp. The signature is returned in a newly allocated ECDSA_SIG structure (or NULL on error). ​ECDSA_do_verify() verifies that the signature sig is a valid ​ECDSA signature of the hash value dgst of size dgst_len using the public key eckey.
RETURN VALUES​ECDSA_size() returns the maximum length signature or 0 on error. ​ECDSA_sign_setup() and ECDSA_sign() return 1 if successful or 0 on error. ​ECDSA_verify() and ECDSA_do_verify() return 1 for a valid signature, 0 for an invalid signature and −1 on error. The error codes can be obtained by ERR_get_error (3).
EXAMPLESCreating a ECDSA signature of given SHA−1 hash value using the named curve secp192k1. First step: create a EC_KEY object (note: this part is not ECDSA specific) ​ int ret; ​ ECDSA_SIG *sig; ​ EC_KEY *eckey = EC_KEY_new(); ​ if (eckey == NULL) ​ { ​ /* error */ ​ } ​ key−>group = EC_GROUP_new_by_nid(NID_secp192k1); ​ if (key−>group == NULL) ​ { ​ /* error */ ​ } ​ if (!EC_KEY_generate_key(eckey)) ​ { ​ /* error */ ​ } Second step: compute the ECDSA signature of a SHA−1 hash value using ECDSA_do_sign ​ sig = ECDSA_do_sign(digest, 20, eckey); ​ if (sig == NULL) ​ { ​ /* error */ ​ } or using ECDSA_sign ​ unsigned char *buffer, *pp; ​ int buf_len; ​ buf_len = ECDSA_size(eckey); ​ buffer = OPENSSL_malloc(buf_len); ​ pp = buffer; ​ if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey); ​ { ​ /* error */ ​ } Third step: verify the created ECDSA signature using ECDSA_do_verify ​ ret = ECDSA_do_verify(digest, 20, sig, eckey); or using ECDSA_verify ​ ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey); and finally evaluate the return value: ​ if (ret == −1) ​ { ​ /* error */ ​ } ​ else if (ret == 0) ​ { ​ /* incorrect signature */ ​ } ​ else /* ret == 1 */ ​ { ​ /* signature ok */ ​ }
CONFORMING TO​ANSI X9.62, US Federal Information Processing Standard FIPS 186−2 (Digital Signature Standard, DSS)
SEE ALSO​dsa (3), rsa (3)
HISTORYThe ecdsa implementation was first introduced in OpenSSL 0.9.8
AUTHORNils Larsch for the OpenSSL project (http://www.openssl.org). 0
Johanes Gumabo
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