focal (3) EVP_PKEY_decrypt_init.3ssl.gz

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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 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>.