--- name: "ecdsa" section: "3ssl" platform: "linux" package: "libssl-doc" version: "1.0.1t-1+deb8u8" release: "Debian 8 (Jessie)" platforms: ["linux"] url: "https://new.carta.tech/ecdsa" --- # ecdsa(3ssl) Elliptic Curve Digital Signature Algorithm ## NAME ecdsa - Elliptic Curve Digital Signature Algorithm ## SYNOPSIS ``` #include 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); ``` ## DESCRIPTION The **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 **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). ## EXAMPLES Creating 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; eckey = EC_KEY_new_by_curve_name(NID_secp192k1); if (eckey == 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) ## HISTORY The ecdsa implementation was first introduced in OpenSSL 0.9.8 ## AUTHOR Nils Larsch for the OpenSSL project (http://www.openssl.org).