NAME¶

EVP_PKEY_decrypt_init, EVP_PKEY_decrypt - decrypt using a public key algorithm

SYNOPSIS¶

 #include <openssl/evp.h>
 int EVP_PKEY_decrypt_init(EVP_PKEY_CTX *ctx);
 int EVP_PKEY_decrypt(EVP_PKEY_CTX *ctx,
                      unsigned char *out, size_t *outlen,
                      const unsigned char *in, size_t inlen);

DESCRIPTION¶

The EVP_PKEY_decrypt_init() function initializes a public key algorithm context using key pkey for a decryption operation.

The EVP_PKEY_decrypt() function performs a public key decryption operation using ctx. The data to be decrypted is specified using the in and inlen parameters. If out is NULL then the maximum size of the output buffer is written to the outlen parameter. If out is not NULL then before the call the outlen parameter should contain the length of the out buffer, if the call is successful the decrypted data is written to out and the amount of data written to outlen.

NOTES¶

After the call to EVP_PKEY_decrypt_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation.

The function EVP_PKEY_decrypt() can be called more than once on the same context if several operations are performed using the same parameters.

RETURN VALUES¶

EVP_PKEY_decrypt_init() and EVP_PKEY_decrypt() return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm.

WARNINGS¶

In OpenSSL versions before 3.1.0, when used in PKCS#1 v1.5 padding, both the return value from the EVP_PKEY_decrypt() and the outlen provided information useful in mounting a Bleichenbacher attack against the used private key. They had to processed in a side-channel free way.

Since version 3.1.0, the EVP_PKEY_decrypt() method when used with PKCS#1 v1.5 padding doesn't return an error in case it detects an error in padding, instead it returns a pseudo-randomly generated message, removing the need of side-channel secure code from applications using OpenSSL.

EXAMPLES¶

Decrypt data using OAEP (for RSA keys):

 #include <openssl/evp.h>
 #include <openssl/rsa.h>
 EVP_PKEY_CTX *ctx;
 ENGINE *eng;
 unsigned char *out, *in;
 size_t outlen, inlen;
 EVP_PKEY *key;
 /*
  * NB: assumes key, eng, in, inlen are already set up
  * and that key is an RSA private key
  */
 ctx = EVP_PKEY_CTX_new(key, eng);
 if (!ctx)
     /* Error occurred */
 if (EVP_PKEY_decrypt_init(ctx) <= 0)
     /* Error */
 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_OAEP_PADDING) <= 0)
     /* Error */
 /* Determine buffer length */
 if (EVP_PKEY_decrypt(ctx, NULL, &outlen, in, inlen) <= 0)
     /* Error */
 out = OPENSSL_malloc(outlen);
 if (!out)
     /* malloc failure */
 if (EVP_PKEY_decrypt(ctx, out, &outlen, in, inlen) <= 0)
     /* Error */
 /* Decrypted data is outlen bytes written to buffer out */

SEE ALSO¶

EVP_PKEY_CTX_new(3), EVP_PKEY_encrypt(3), EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3), EVP_PKEY_derive(3)

HISTORY¶

These functions were added in OpenSSL 1.0.0.

COPYRIGHT¶

Copyright 2006-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.