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.IX Title "EVP_SIGNINIT 1"
.TH EVP_SIGNINIT 1 "perl v5.6.1" "2000-11-13" "User Contributed Perl Documentation"
.UC
.SH "NAME"
EVP_SignInit, EVP_SignUpdate, EVP_SignFinal \- \s-1EVP\s0 signing functions
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
.Ve
.Vb 3
\& void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
\& void EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
\& int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
.Ve
.Vb 1
\& int EVP_PKEY_size(EVP_PKEY *pkey);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1EVP\s0 signature routines are a high level interface to digital
signatures.
.PP
\&\fIEVP_SignInit()\fR initializes a signing context \fBctx\fR to using digest
\&\fBtype\fR: this will typically be supplied by a function such as
\&\fIEVP_sha1()\fR.
.PP
\&\fIEVP_SignUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
signature context \fBctx\fR. This function can be called several times on the
same \fBctx\fR to include additional data.
.PP
\&\fIEVP_SignFinal()\fR signs the data in \fBctx\fR using the private key \fBpkey\fR
and places the signature in \fBsig\fR. If the \fBs\fR parameter is not \s-1NULL\s0
then the number of bytes of data written (i.e. the length of the signature)
will be written to the integer at \fBs\fR, at most EVP_PKEY_size(pkey) bytes
will be written.  After calling \fIEVP_SignFinal()\fR no additional calls to
\&\fIEVP_SignUpdate()\fR can be made, but \fIEVP_SignInit()\fR can be called to initialize
a new signature operation.
.PP
\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes. The actual
signature returned by \fIEVP_SignFinal()\fR may be smaller.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIEVP_SignInit()\fR and \fIEVP_SignUpdate()\fR do not return values.
.PP
\&\fIEVP_SignFinal()\fR returns 1 for success and 0 for failure.
.PP
\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes.
.PP
The error codes can be obtained by ERR_get_error(3).
.SH "NOTES"
.IX Header "NOTES"
The \fB\s-1EVP\s0\fR 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.
.PP
Due to the link between message digests and public key algorithms the correct
digest algorithm must be used with the correct public key type. A list of
algorithms and associated public key algorithms appears in 
EVP_DigestInit(3).
.PP
When signing with \s-1DSA\s0 private keys the random number generator must be seeded
or the operation will fail. The random number generator does not need to be
seeded for \s-1RSA\s0 signatures.
.SH "BUGS"
.IX Header "BUGS"
Several of the functions do not return values: maybe they should. Although the
internal digest operations will never fail some future hardware based operations
might.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
EVP_VerifyInit(3),
EVP_DigestInit(3), err(3),
evp(3), hmac(3), md2(3),
md5(3), mdc2(3), ripemd(3),
sha(3), digest(1)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIEVP_SignInit()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR are
available in all versions of SSLeay and OpenSSL.