ECDSA_SIG_NEW(3ossl)

🌸 NAME 🌸

okay bestie, welcome to ECDSA_SIG_NEW(3ossl) — the OpenSSL manual page for all the little functions that create, destroy, and poke at ECDSA_SIG objects 💅

The whole squad is:

• ECDSA_SIG_new()
• ECDSA_SIG_free()
• ECDSA_SIG_get0()
• ECDSA_SIG_get0_r()
• ECDSA_SIG_get0_s()
• ECDSA_SIG_set0()

They’re the functions for creating, destroying, and manipulating ECDSA_SIG objects. Slay.

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✨ SYNOPSIS ✨

        #include <openssl/ecdsa.h>

        ECDSA_SIG *ECDSA_SIG_new(void);
        void ECDSA_SIG_free(ECDSA_SIG *sig);
        void ECDSA_SIG_get0(const ECDSA_SIG *sig, const BIGNUM **pr, const BIGNUM **ps);
        const BIGNUM *ECDSA_SIG_get0_r(const ECDSA_SIG *sig);
        const BIGNUM *ECDSA_SIG_get0_s(const ECDSA_SIG *sig);
        int ECDSA_SIG_set0(ECDSA_SIG *sig, BIGNUM *r, BIGNUM *s);

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🦋 DESCRIPTION 🦋

ECDSA_SIG is an opaque structure made of two BIGNUMs: one for the r value and one for the s value of an Elliptic Curve Digital Signature Algorithm (ECDSA) signature — peep FIPS186-4 or X9.62 for the lore 📚

The ECDSA_SIG object was mainly used by the deprecated low-level functions described in ECDSA_sign(3). It is still required in order to be able to set or get the values of r and s into or from a signature. This is mainly used for testing purposes, as shown in the EXAMPLES 👀

ECDSA_SIG_new() allocates an empty ECDSA_SIG structure. ⚠️ Note: before OpenSSL 1.1.0, the r and s components were initialised.

ECDSA_SIG_free() frees the ECDSA_SIG structure sig. If the argument is NULL, nothing is done. Easy peasy 🫶

ECDSA_SIG_get0() returns internal pointers to the r and s values contained in sig and stores them in *pr and *ps, respectively. The pointer pr or ps can be NULL, in which case the corresponding value is not returned.

The values r and s can also be retrieved separately by the corresponding function ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s(), respectively.

Non-NULL r and s values can be set on the sig by calling ECDSA_SIG_set0(). Calling this function transfers the memory management of the values to the ECDSA_SIG object, and therefore the values that have been passed in should not be freed by the caller. No double-free chaos, bestie 💀

See i2d_ECDSA_SIG(3) and d2i_ECDSA_SIG(3) for information about encoding and decoding ECDSA signatures to/from DER.

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💖 RETURN VALUES 💖

• ECDSA_SIG_new() returns NULL if the allocation fails.
• ECDSA_SIG_set0() returns 1 on success or 0 on failure.
• ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s() return the corresponding value, or NULL if it is unset.

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🌈 EXAMPLES 🌈

First up: extract the signature r and s values from an ECDSA signature of size signaturelen ⭐

        ECDSA_SIG *obj;
        const BIGNUM *r, *s;

        /* Load a signature into the ECDSA_SIG object */
        obj = d2i_ECDSA_SIG(NULL, &signature, signaturelen);
        if (obj == NULL)
            /* error */

        r = ECDSA_SIG_get0_r(obj);
        s = ECDSA_SIG_get0_s(obj);
        if (r == NULL || s == NULL)
            /* error */

        /* Use BN_bn2binpad() here to convert to r and s into byte arrays */

        /*
         * Do not try to access I<r> or I<s> after calling ECDSA_SIG_free(),
         * as they are both freed by this call.
         */
        ECDSA_SIG_free(obj);

Next: convert r and s byte arrays into an ECDSA_SIG signature of size signaturelen 🎀

        ECDSA_SIG *obj = NULL;
        unsigned char *signature = NULL;
        size_t signaturelen;
        BIGNUM *rbn = NULL, *sbn = NULL;

        obj = ECDSA_SIG_new();
        if (obj == NULL)
            /* error */
        rbn = BN_bin2bn(r, rlen, NULL);
        sbn = BN_bin2bn(s, slen, NULL);
        if (rbn == NULL || sbn == NULL)
            /* error */

        if (!ECDSA_SIG_set0(obj, rbn, sbn))
            /* error */
        /* Set these to NULL since they are now owned by obj */
        rbn = sbn = NULL;

        signaturelen = i2d_ECDSA_SIG(obj, &signature);
        if (signaturelen <= 0)
            /* error */

        /*
         * This signature could now be passed to L<EVP_DigestVerify(3)>
         * or L<EVP_DigestVerifyFinal(3)>
         */

        BN_free(rbn);
        BN_free(sbn);
        OPENSSL_free(signature);
        ECDSA_SIG_free(obj);

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👑 CONFORMING TO 👑

ANSI X9.62, US Federal Information Processing Standard FIPS186-4 (Digital Signature Standard, DSS) — standards girlies stay winning 💜

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🧚 SEE ALSO 🧚

• EC_KEY_new(3)
• EVP_DigestSignInit(3)
• EVP_DigestVerifyInit(3)
• EVP_PKEY_sign(3)
• i2d_ECDSA_SIG(3)
• d2i_ECDSA_SIG(3)
• ECDSA_sign(3)

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🍓 COPYRIGHT 🍓

Copyright 2004-2024 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.

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mwah 💋 that’s the whole page — from OpenSSL 3.5.6, dated 2026-04-07. byeee bestie 🫶