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EVP_PKEY_DECRYPT(3ossl)             OpenSSL            EVP_PKEY_DECRYPT(3ossl)



NAME

       EVP_PKEY_decrypt_init, EVP_PKEY_decrypt_init_ex, 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_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
        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_init_ex() function initializes a public key
       algorithm context using key pkey for a decryption operation and sets
       the algorithm specific params.

       The EVP_PKEY_decrypt(3) 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 minimum required size of
       the output buffer is written to the *outlen parameter.

       If out is not NULL then before the call the *outlen parameter must
       contain the length of the out buffer. If the call is successful the
       decrypted data is written to out and the amount of the decrypted data
       written to *outlen, otherwise an error is returned.


NOTES

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

       The function EVP_PKEY_decrypt(3) 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(), EVP_PKEY_decrypt_init_ex() and
       EVP_PKEY_decrypt(3) 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 3.2.0, when used in PKCS#1 v1.5 padding,
       both the return value from the EVP_PKEY_decrypt(3) 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 3.2.0, the EVP_PKEY_decrypt(3) 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_PKCS1_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 2006-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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>.

3.2.0                             2023-11-23           EVP_PKEY_DECRYPT(3ossl)

openssl 3.2.0 - Generated Sat Dec 2 05:55:17 CST 2023
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