--- /dev/null
+=pod
+
+=head1 NAME
+
+EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions
+
+=head1 SYNOPSIS
+
+ #include <openssl/evp.h>
+
+ int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
+ int 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);
+
+ void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
+
+ int EVP_PKEY_size(EVP_PKEY *pkey);
+
+=head1 DESCRIPTION
+
+The EVP signature routines are a high level interface to digital
+signatures.
+
+EVP_SignInit_ex() sets up signing context B<ctx> to use digest
+B<type> from ENGINE B<impl>. B<ctx> must be initialized with
+EVP_MD_CTX_init() before calling this function.
+
+EVP_SignUpdate() 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.
+
+EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and
+places the signature in B<sig>. B<sig> must be at least EVP_PKEY_size(pkey)
+bytes in size. B<s> is an OUT paramter, and not used as an IN parameter.
+The number of bytes of data written (i.e. the length of the signature)
+will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes
+will be written.
+
+EVP_SignInit() initializes a signing context B<ctx> to use the default
+implementation of digest B<type>.
+
+EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual
+signature returned by EVP_SignFinal() may be smaller.
+
+=head1 RETURN VALUES
+
+EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1
+for success and 0 for failure.
+
+EVP_PKEY_size() returns the maximum size of a signature in bytes.
+
+The error codes can be obtained by 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.
+
+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
+L<EVP_DigestInit(3)|EVP_DigestInit(3)>.
+
+When signing with DSA 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 RSA signatures.
+
+The call to EVP_SignFinal() internally finalizes a copy of the digest context.
+This means that calls to EVP_SignUpdate() and EVP_SignFinal() 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.
+
+=head1 BUGS
+
+Older versions of this documentation wrongly stated that calls to
+EVP_SignUpdate() could not be made after calling EVP_SignFinal().
+
+Since the private key is passed in the call to EVP_SignFinal() any error
+relating to the private key (for example an unsuitable key and digest
+combination) will not be indicated until after potentially large amounts of
+data have been passed through EVP_SignUpdate().
+
+It is not possible to change the signing parameters using these function.
+
+The previous two bugs are fixed in the newer EVP_SignDigest*() function.
+
+=head1 SEE ALSO
+
+L<EVP_VerifyInit(3)|EVP_VerifyInit(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_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
+available in all versions of SSLeay and OpenSSL.
+
+EVP_SignInit_ex() was added in OpenSSL 0.9.7.
+
+=cut
projects / cassiopeia.git / blobdiff