Edit File: EVP_PKEY_sign_init.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" EVP_PKEY_sign_init, EVP_PKEY_sign \- sign using a public key algorithm .SH "SYNOPSIS" .IX 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 .SH "DESCRIPTION" .IX Header "DESCRIPTION" The \fBEVP_PKEY_sign_init()\fR function initializes a public key algorithm context using key \fBpkey\fR for a signing operation. .PP The \fBEVP_PKEY_sign()\fR function performs a public key signing operation using \fBctx\fR. The data to be signed is specified using the \fBtbs\fR and \&\fBtbslen\fR parameters. If \fBsig\fR is \fB\s-1NULL\s0\fR then the maximum size of the output buffer is written to the \fBsiglen\fR parameter. If \fBsig\fR is not \fB\s-1NULL\s0\fR then before the call the \fBsiglen\fR parameter should contain the length of the \&\fBsig\fR buffer, if the call is successful the signature is written to \&\fBsig\fR and the amount of data written to \fBsiglen\fR. .SH "NOTES" .IX Header "NOTES" \&\fBEVP_PKEY_sign()\fR does not hash the data to be signed, and therefore is normally used to sign digests. For signing arbitrary messages, see the \&\fBEVP_DigestSignInit\fR\|(3) and \&\fBEVP_SignInit\fR\|(3) signing interfaces instead. .PP After the call to \fBEVP_PKEY_sign_init()\fR algorithm specific control operations can be performed to set any appropriate parameters for the operation (see \fBEVP_PKEY_CTX_ctrl\fR\|(3)). .PP The function \fBEVP_PKEY_sign()\fR can be called more than once on the same context if several operations are performed using the same parameters. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBEVP_PKEY_sign_init()\fR and \fBEVP_PKEY_sign()\fR 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. .SH "EXAMPLE" .IX Header "EXAMPLE" Sign data using \s-1RSA\s0 with PKCS#1 padding and \s-1SHA256\s0 digest: .PP .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 .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBEVP_PKEY_CTX_new\fR\|(3), \&\fBEVP_PKEY_CTX_ctrl\fR\|(3), \&\fBEVP_PKEY_encrypt\fR\|(3), \&\fBEVP_PKEY_decrypt\fR\|(3), \&\fBEVP_PKEY_verify\fR\|(3), \&\fBEVP_PKEY_verify_recover\fR\|(3), \&\fBEVP_PKEY_derive\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" These functions were first added to OpenSSL 1.0.0.