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- =pod
- =head1 NAME
- RSA_private_encrypt, RSA_public_decrypt - low level signature operations
- =head1 SYNOPSIS
- #include <openssl/rsa.h>
- int RSA_private_encrypt(int flen, unsigned char *from,
- unsigned char *to, RSA *rsa, int padding);
- int RSA_public_decrypt(int flen, unsigned char *from,
- unsigned char *to, RSA *rsa, int padding);
- =head1 DESCRIPTION
- These functions handle RSA signatures at a low level.
- RSA_private_encrypt() signs the B<flen> bytes at B<from> (usually a
- message digest with an algorithm identifier) using the private key
- B<rsa> and stores the signature in B<to>. B<to> must point to
- B<RSA_size(rsa)> bytes of memory.
- B<padding> denotes one of the following modes:
- =over 4
- =item RSA_PKCS1_PADDING
- PKCS #1 v1.5 padding. This function does not handle the
- B<algorithmIdentifier> specified in PKCS #1. When generating or
- verifying PKCS #1 signatures, L<RSA_sign(3)|RSA_sign(3)> and L<RSA_verify(3)|RSA_verify(3)> should be
- used.
- =item RSA_NO_PADDING
- Raw RSA signature. This mode should I<only> be used to implement
- cryptographically sound padding modes in the application code.
- Signing user data directly with RSA is insecure.
- =back
- RSA_public_decrypt() recovers the message digest from the B<flen>
- bytes long signature at B<from> using the signer's public key
- B<rsa>. B<to> must point to a memory section large enough to hold the
- message digest (which is smaller than B<RSA_size(rsa) -
- 11>). B<padding> is the padding mode that was used to sign the data.
- =head1 RETURN VALUES
- RSA_private_encrypt() returns the size of the signature (i.e.,
- RSA_size(rsa)). RSA_public_decrypt() returns the size of the
- recovered message digest.
- On error, -1 is returned; the error codes can be
- obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
- =head1 SEE ALSO
- L<ERR_get_error(3)|ERR_get_error(3)>, L<rsa(3)|rsa(3)>,
- L<RSA_sign(3)|RSA_sign(3)>, L<RSA_verify(3)|RSA_verify(3)>
- =head1 HISTORY
- The B<padding> argument was added in SSLeay 0.8. RSA_NO_PADDING is
- available since SSLeay 0.9.0.
- =cut
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