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Title "EVP_PKEY_SIGN 3"
EVP_PKEY_SIGN 3 "2020-04-21" "1.1.1g" "OpenSSL"
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"NAME"
EVP_PKEY_sign_init, EVP_PKEY_sign - sign using a public key algorithm
"SYNOPSIS"
Header "SYNOPSIS" .Vb 1 #include <openssl/evp.h> \& int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx); int EVP_PKEY_sign(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen, const unsigned char *tbs, size_t tbslen); .Ve
"DESCRIPTION"
Header "DESCRIPTION" The EVP_PKEY_sign_init() function initializes a public key algorithm context using key pkey for a signing operation.

The EVP_PKEY_sign() function performs a public key signing operation using ctx. The data to be signed is specified using the tbs and \fBtbslen parameters. If sig is \s-1NULL\s0 then the maximum size of the output buffer is written to the siglen parameter. If sig is not \s-1NULL\s0 then before the call the siglen parameter should contain the length of the \fBsig buffer, if the call is successful the signature is written to \fBsig and the amount of data written to siglen.

"NOTES"
Header "NOTES" \fBEVP_PKEY_sign() does not hash the data to be signed, and therefore is normally used to sign digests. For signing arbitrary messages, see the \fBEVP_DigestSignInit\|(3) and \fBEVP_SignInit\|(3) signing interfaces instead.

After the call to EVP_PKEY_sign_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation (see EVP_PKEY_CTX_ctrl\|(3)).

The function EVP_PKEY_sign() can be called more than once on the same context if several operations are performed using the same parameters.

"RETURN VALUES"
Header "RETURN VALUES" \fBEVP_PKEY_sign_init() and EVP_PKEY_sign() return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm.
"EXAMPLES"
Header "EXAMPLES" Sign data using \s-1RSA\s0 with PKCS#1 padding and \s-1SHA256\s0 digest:

.Vb 2 #include <openssl/evp.h> #include <openssl/rsa.h> \& EVP_PKEY_CTX *ctx; /* md is a SHA-256 digest in this example. */ unsigned char *md, *sig; size_t mdlen = 32, siglen; EVP_PKEY *signing_key; \& /* * NB: assumes signing_key and md are set up before the next * step. signing_key must be an RSA private key and md must * point to the SHA-256 digest to be signed. */ ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */); if (!ctx) /* Error occurred */ if (EVP_PKEY_sign_init(ctx) <= 0) /* Error */ if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) /* Error */ if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) /* Error */ \& /* Determine buffer length */ if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0) /* Error */ \& sig = OPENSSL_malloc(siglen); \& if (!sig) /* malloc failure */ \& if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0) /* Error */ \& /* Signature is siglen bytes written to buffer sig */ .Ve

"SEE ALSO"
Header "SEE ALSO" \fBEVP_PKEY_CTX_new\|(3), \fBEVP_PKEY_CTX_ctrl\|(3), \fBEVP_PKEY_encrypt\|(3), \fBEVP_PKEY_decrypt\|(3), \fBEVP_PKEY_verify\|(3), \fBEVP_PKEY_verify_recover\|(3), \fBEVP_PKEY_derive\|(3)
"HISTORY"
Header "HISTORY" These functions were added in OpenSSL 1.0.0.
"COPYRIGHT"
Header "COPYRIGHT" Copyright 2006-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.