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-=pod
-
-=head1 NAME
-
-EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP signing functions
-
-=head1 SYNOPSIS
-
- #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);
-
-=head1 DESCRIPTION
-
-The EVP signature routines are a high level interface to digital signatures.
-
-EVP_DigestSignInit() sets up signing context B<ctx> to use digest B<type> from
-ENGINE B<impl> and private key B<pkey>. B<ctx> must be initialized with
-EVP_MD_CTX_init() before calling this function. If B<pctx> is not NULL the
-EVP_PKEY_CTX of the signing operation will be written to B<*pctx>: this can
-be used to set alternative signing options.
-
-EVP_DigestSignUpdate() hashes B<cnt> bytes of data at B<d> into the
-signature context B<ctx>. This function can be called several times on the
-same B<ctx> to include additional data. This function is currently implemented
-usig a macro.
-
-EVP_DigestSignFinal() signs the data in B<ctx> places the signature in B<sig>.
-If B<sig> is B<NULL> then the maximum size of the output buffer is written to
-the B<siglen> parameter. If B<sig> is not B<NULL> then before the call the
-B<siglen> parameter should contain the length of the B<sig> buffer, if the
-call is successful the signature is written to B<sig> and the amount of data
-written to B<siglen>.
-
-=head1 RETURN VALUES
-
-EVP_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 L<ERR_get_error(3)|ERR_get_error(3)>.
-
-=head1 NOTES
-
-The B<EVP> 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 "clone" digests such as EVP_dss1()
-needed to be used to sign using SHA1 and DSA. 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
-EVP_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.
-
-=head1 SEE ALSO
-
-L<EVP_DigestVerifyInit(3)|EVP_DigestVerifyInit(3)>,
-L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>,
-L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
-L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
-L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)>
-
-=head1 HISTORY
-
-EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
-were first added to OpenSSL 1.0.0.
-
-=cut