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EVP_PKEY_DECRYPT(3)                 OpenSSL                EVP_PKEY_DECRYPT(3)
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>;.
1.1.1k                            2024-10-09               EVP_PKEY_DECRYPT(3)