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105 lines
3.6 KiB
105 lines
3.6 KiB
14 years ago
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=pod
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=head1 NAME
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EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
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void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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int EVP_PKEY_size(EVP_PKEY *pkey);
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=head1 DESCRIPTION
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The EVP signature routines are a high level interface to digital
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signatures.
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EVP_SignInit_ex() sets up signing context B<ctx> to use digest
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B<type> from ENGINE B<impl>. B<ctx> must be initialized with
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EVP_MD_CTX_init() before calling this function.
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EVP_SignUpdate() 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.
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EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and
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places the signature in B<sig>. The number of bytes of data written (i.e. the
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length of the signature) will be written to the integer at B<s>, at most
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EVP_PKEY_size(pkey) bytes will be written.
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EVP_SignInit() initializes a signing context B<ctx> to use the default
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implementation of digest B<type>.
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EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual
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signature returned by EVP_SignFinal() may be smaller.
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=head1 RETURN VALUES
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EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1
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for success and 0 for failure.
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EVP_PKEY_size() returns the maximum size of a signature in bytes.
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The error codes can be obtained by 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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Due to the link between message digests and public key algorithms the correct
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digest algorithm must be used with the correct public key type. A list of
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algorithms and associated public key algorithms appears in
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L<EVP_DigestInit(3)|EVP_DigestInit(3)>.
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When signing with DSA private keys the random number generator must be seeded
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or the operation will fail. The random number generator does not need to be
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seeded for RSA signatures.
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The call to EVP_SignFinal() internally finalizes a copy of the digest context.
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This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called
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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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=head1 BUGS
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Older versions of this documentation wrongly stated that calls to
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EVP_SignUpdate() could not be made after calling EVP_SignFinal().
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Since the private key is passed in the call to EVP_SignFinal() any error
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relating to the private key (for example an unsuitable key and digest
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combination) will not be indicated until after potentially large amounts of
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data have been passed through EVP_SignUpdate().
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It is not possible to change the signing parameters using these function.
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The previous two bugs are fixed in the newer EVP_SignDigest*() function.
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=head1 SEE ALSO
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L<EVP_VerifyInit(3)|EVP_VerifyInit(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_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
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available in all versions of SSLeay and OpenSSL.
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EVP_SignInit_ex() was added in OpenSSL 0.9.7.
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=cut
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