- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- SEE ALSO
- HISTORY

# NAME

RSA_private_encrypt, RSA_public_decrypt - low level signature operations

# 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);

# DESCRIPTION

These functions handle RSA signatures at a low level.

`RSA_private_encrypt()` signs the flen bytes at from (usually a message digest with an algorithm identifier) using the private key rsa and stores the signature in to. to must point to RSA_size(rsa) bytes of memory.

padding denotes one of the following modes:

RSA_PKCS1_PADDING

  PKCS #1 v1.5 padding. This function does not handle the algorithmIdentifier specified in PKCS #1. When generating or verifying PKCS #1 signatures, RSA_sign and RSA_verify should be used.

RSA_NO_PADDING

  Raw RSA signature. This mode should only be used to implement cryptographically sound padding modes in the application code. Signing user data directly with RSA is insecure.

`RSA_public_decrypt()` recovers the message digest from the flen bytes long signature at from using the signer's public key rsa. to must point to a memory section large enough to hold the message digest (which is smaller than RSA_size(rsa) - 11). padding is the padding mode that was used to sign the data.

# 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 ERR_get_error.

# SEE ALSO

ERR_get_error, rsa, RSA_sign, RSA_verify

# HISTORY

The padding argument was added in SSLeay 0.8. RSA_NO_PADDING is available since SSLeay 0.9.0.