| =pod |
| |
| =head1 NAME |
| |
| EVP_SignInit, EVP_SignInit_ex, 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 |