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Title "EVP_DigestSignInit 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP signing functions Header "SYNOPSIS" .Vb 1 #include <openssl/evp.h> \& int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt); int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen); .Ve Header "DESCRIPTION" The \s-1EVP\s0 signature routines are a high level interface to digital signatures.

\fIEVP_DigestSignInit() sets up signing context ctx to use digest type from \s-1ENGINE \s0impl and private key pkey. ctx must be initialized with \fIEVP_MD_CTX_init() before calling this function. If pctx is not \s-1NULL\s0 the \s-1EVP_PKEY_CTX\s0 of the signing operation will be written to *pctx: this can be used to set alternative signing options.

\fIEVP_DigestSignUpdate() hashes cnt bytes of data at d into the signature context ctx. This function can be called several times on the same ctx to include additional data. This function is currently implemented usig a macro.

\fIEVP_DigestSignFinal() signs the data in ctx places the signature in sig. 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 \fBsiglen parameter should contain the length of the sig buffer, if the call is successful the signature is written to sig and the amount of data written to siglen.

Header "RETURN VALUES" \fIEVP_DigestSignInit() EVP_DigestSignUpdate() and EVP_DigestSignaFinal() 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.

The error codes can be obtained from ERR_get_error\|(3).

Header "NOTES" The \s-1EVP\s0 interface to digital signatures should almost always be used in preference to the low level interfaces. This is because the code then becomes transparent to the algorithm used and much more flexible.

In previous versions of OpenSSL there was a link between message digest types and public key algorithms. This meant that \*(L"clone\*(R" digests such as EVP_dss1() needed to be used to sign using \s-1SHA1\s0 and \s-1DSA.\s0 This is no longer necessary and the use of clone digest is now discouraged.

For some key types and parameters the random number generator must be seeded or the operation will fail.

The call to EVP_DigestSignFinal() internally finalizes a copy of the digest context. This means that calls to EVP_DigestSignUpdate() and \fIEVP_DigestSignFinal() can be called later to digest and sign additional data.

Since only a copy of the digest context is ever finalized the context must be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak will occur.

The use of EVP_PKEY_size() with these functions is discouraged because some signature operations may have a signature length which depends on the parameters set. As a result EVP_PKEY_size() would have to return a value which indicates the maximum possible signature for any set of parameters.

Header "SEE ALSO" \fIEVP_DigestVerifyInit\|(3), \fIEVP_DigestInit\|(3), err\|(3), \fIevp\|(3), hmac\|(3), md2\|(3), \fImd5\|(3), mdc2\|(3), ripemd\|(3), \fIsha\|(3), dgst\|(1) Header "HISTORY" \fIEVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal() were first added to OpenSSL 1.0.0.