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87 lines
3.5 KiB
87 lines
3.5 KiB
=pod
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=head1 NAME
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EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP signing functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
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int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
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=head1 DESCRIPTION
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The EVP signature routines are a high level interface to digital signatures.
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EVP_DigestSignInit() sets up signing context B<ctx> to use digest B<type> from
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ENGINE B<impl> and private key B<pkey>. B<ctx> must be initialized with
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EVP_MD_CTX_init() before calling this function. If B<pctx> is not NULL the
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EVP_PKEY_CTX of the signing operation will be written to B<*pctx>: this can
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be used to set alternative signing options.
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EVP_DigestSignUpdate() hashes B<cnt> bytes of data at B<d> into the
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signature context B<ctx>. This function can be called several times on the
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same B<ctx> to include additional data. This function is currently implemented
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usig a macro.
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EVP_DigestSignFinal() signs the data in B<ctx> places the signature in B<sig>.
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If B<sig> is B<NULL> then the maximum size of the output buffer is written to
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the B<siglen> parameter. If B<sig> is not B<NULL> then before the call the
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B<siglen> parameter should contain the length of the B<sig> buffer, if the
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call is successful the signature is written to B<sig> and the amount of data
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written to B<siglen>.
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=head1 RETURN VALUES
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EVP_DigestSignInit() EVP_DigestSignUpdate() and EVP_DigestSignaFinal() return
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1 for success and 0 or a negative value for failure. In particular a return
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value of -2 indicates the operation is not supported by the public key
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algorithm.
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The error codes can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>.
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=head1 NOTES
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The B<EVP> interface to digital signatures should almost always be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the algorithm used and much more flexible.
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In previous versions of OpenSSL there was a link between message digest types
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and public key algorithms. This meant that "clone" digests such as EVP_dss1()
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needed to be used to sign using SHA1 and DSA. This is no longer necessary and
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the use of clone digest is now discouraged.
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For some key types and parameters the random number generator must be seeded
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or the operation will fail.
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The call to EVP_DigestSignFinal() internally finalizes a copy of the digest
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context. This means that calls to EVP_DigestSignUpdate() and
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EVP_DigestSignFinal() can be called later to digest and sign additional data.
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Since only a copy of the digest context is ever finalized the context must
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be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak
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will occur.
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The use of EVP_PKEY_size() with these functions is discouraged because some
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signature operations may have a signature length which depends on the
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parameters set. As a result EVP_PKEY_size() would have to return a value
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which indicates the maximum possible signature for any set of parameters.
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=head1 SEE ALSO
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L<EVP_DigestVerifyInit(3)|EVP_DigestVerifyInit(3)>,
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L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>,
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L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
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L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
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L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)>
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=head1 HISTORY
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EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
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were first added to OpenSSL 1.0.0.
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=cut
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