EVP_PKEY-RSA(7)

NAME
EVP_PKEY-RSA, EVP_KEYMGMT-RSA, RSA - EVP_PKEY RSA keytype and algorithm support

DESCRIPTION
The RSA keytype is implemented in OpenSSL's default and FIPS providers. That implementation supports the basic RSA keys, containing the modulus n, the public exponent e, the private exponent d, and a collection of prime factors, exponents and coefficient for CRT calculations, of which the first few are known as p and q, dP and dQ, and qInv.

RSA key generation uses FIPS 186-5 Section A.1.6 "Generation of Probable Primes with Conditions Based on Auxiliary Probable Primes" for the OpenSSL FIPS provider. It is also used for the OpenSSL default provider when the generation parameters satisfy the following conditions:

There are 2 "primes" (p, q)
The exponent "e" >= 65537 and is odd
The cryptographic length "bits" >= 2048

Otherwise the OpenSSL default provider uses an older general multi-prime key generator.

  Common RSA parameters
In addition to the common parameters that all keytypes should support (see "Common parameters" in provider-keymgmt(7)), the RSA keytype implementation supports the following.

"n" (OSSL_PKEY_PARAM_RSA_N) <unsigned integer>
    The RSA modulus "n" value.

"e" (OSSL_PKEY_PARAM_RSA_E) <unsigned integer>
    The RSA public exponent "e" value. This value must always be set when creating a raw key using EVP_PKEY_fromdata(3). Note that when a decryption operation is performed, that this value is used for blinding purposes to prevent timing attacks.

"d" (OSSL_PKEY_PARAM_RSA_D) <unsigned integer>
    The RSA private exponent "d" value.

"rsa-factor1" (OSSL_PKEY_PARAM_RSA_FACTOR1) <unsigned integer>
"rsa-factor2" (OSSL_PKEY_PARAM_RSA_FACTOR2) <unsigned integer>
"rsa-factor3" (OSSL_PKEY_PARAM_RSA_FACTOR3) <unsigned integer>
"rsa-factor4" (OSSL_PKEY_PARAM_RSA_FACTOR4) <unsigned integer>
"rsa-factor5" (OSSL_PKEY_PARAM_RSA_FACTOR5) <unsigned integer>
"rsa-factor6" (OSSL_PKEY_PARAM_RSA_FACTOR6) <unsigned integer>
"rsa-factor7" (OSSL_PKEY_PARAM_RSA_FACTOR7) <unsigned integer>
"rsa-factor8" (OSSL_PKEY_PARAM_RSA_FACTOR8) <unsigned integer>
"rsa-factor9" (OSSL_PKEY_PARAM_RSA_FACTOR9) <unsigned integer>
"rsa-factor10" (OSSL_PKEY_PARAM_RSA_FACTOR10) <unsigned integer>
    RSA prime factors. The factors are known as "p", "q" and "r_i" in RFC8017. Up to eight additional "r_i" prime factors are supported.

"rsa-exponent1" (OSSL_PKEY_PARAM_RSA_EXPONENT1) <unsigned integer>
"rsa-exponent2" (OSSL_PKEY_PARAM_RSA_EXPONENT2) <unsigned integer>
"rsa-exponent3" (OSSL_PKEY_PARAM_RSA_EXPONENT3) <unsigned integer>
"rsa-exponent4" (OSSL_PKEY_PARAM_RSA_EXPONENT4) <unsigned integer>
"rsa-exponent5" (OSSL_PKEY_PARAM_RSA_EXPONENT5) <unsigned integer>
"rsa-exponent6" (OSSL_PKEY_PARAM_RSA_EXPONENT6) <unsigned integer>
"rsa-exponent7" (OSSL_PKEY_PARAM_RSA_EXPONENT7) <unsigned integer>
"rsa-exponent8" (OSSL_PKEY_PARAM_RSA_EXPONENT8) <unsigned integer>
"rsa-exponent9" (OSSL_PKEY_PARAM_RSA_EXPONENT9) <unsigned integer>
"rsa-exponent10" (OSSL_PKEY_PARAM_RSA_EXPONENT10) <unsigned integer>
    RSA CRT (Chinese Remainder Theorem) exponents. The exponents are known as "dP", "dQ" and "d_i" in RFC8017. Up to eight additional "d_i" exponents are supported.

"rsa-coefficient1" (OSSL_PKEY_PARAM_RSA_COEFFICIENT1) <unsigned integer>
"rsa-coefficient2" (OSSL_PKEY_PARAM_RSA_COEFFICIENT2) <unsigned integer>
"rsa-coefficient3" (OSSL_PKEY_PARAM_RSA_COEFFICIENT3) <unsigned integer>
"rsa-coefficient4" (OSSL_PKEY_PARAM_RSA_COEFFICIENT4) <unsigned integer>
"rsa-coefficient5" (OSSL_PKEY_PARAM_RSA_COEFFICIENT5) <unsigned integer>
"rsa-coefficient6" (OSSL_PKEY_PARAM_RSA_COEFFICIENT6) <unsigned integer>
"rsa-coefficient7" (OSSL_PKEY_PARAM_RSA_COEFFICIENT7) <unsigned integer>
"rsa-coefficient8" (OSSL_PKEY_PARAM_RSA_COEFFICIENT8) <unsigned integer>
"rsa-coefficient9" (OSSL_PKEY_PARAM_RSA_COEFFICIENT9) <unsigned integer>
    RSA CRT (Chinese Remainder Theorem) coefficients. The coefficients are known as "qInv" and "t_i". Up to eight additional "t_i" exponents are supported.

  RSA key generation parameters
When generating RSA keys, the following key generation parameters may be used.

"bits" (OSSL_PKEY_PARAM_RSA_BITS) <unsigned integer>
    The value should be the cryptographic length for the RSA cryptosystem, in bits.

"primes" (OSSL_PKEY_PARAM_RSA_PRIMES) <unsigned integer>
    The value should be the number of primes for the generated RSA key. The default is 2. It isn't permitted to specify a larger number of primes than 10. Additionally, the number of primes is limited by the length of the key being generated so the maximum number could be less. Some providers may only support a value of 2.

"e" (OSSL_PKEY_PARAM_RSA_E) <unsigned integer>
    The RSA "e" value. The value may be any odd number greater than or equal to 65537. The default value is 65537. For legacy reasons a value of 3 is currently accepted but is deprecated.

"rsa-derive-from-pq"  (OSSL_PKEY_PARAM_RSA_DERIVE_FROM_PQ) <unsigned integer>
    Indicate that missing parameters not passed in the parameter list should be derived if not provided. Setting a nonzero value will cause all needed exponents and coefficients to be derived if not available. Setting this option requires at least OSSL_PARAM_RSA_FACTOR1, OSSL_PARAM_RSA_FACTOR2, and OSSL_PARAM_RSA_N to be provided. This option is ignored if OSSL_KEYMGMT_SELECT_PRIVATE_KEY is not set in the selection parameter.

"rsa-a" (OSSL_PKEY_PARAM_RSA_A) <unsigned integer>
    Setting this value to one of 1, 3, 5 or 7 applies an additional constraint requiring that the computed prime p is congruent to this value mod 8. If this value is zero then it is ignored. An error will occur if the value is not set to one of the above values.

"rsa-b" (OSSL_PKEY_PARAM_RSA_B) <unsigned integer>
    Setting this value to one of 1, 3, 5 or 7 applies an additional constraint requiring that the computed prime q is congruent to this value mod 8. If this value is zero then it is ignored. An error will occur if the value is not set to one of the above values.

  RSA key generation parameters for FIPS module testing
When generating RSA keys, the following additional key generation parameters may be used for algorithm testing purposes only. Do not use these to generate RSA keys for a production environment.

"xp" (OSSL_PKEY_PARAM_RSA_TEST_XP) <unsigned integer>
"xq" (OSSL_PKEY_PARAM_RSA_TEST_XQ) <unsigned integer>
    These 2 fields are normally randomly generated and are used to generate "p" and "q".

"xp1" (OSSL_PKEY_PARAM_RSA_TEST_XP1) <unsigned integer>
"xp2" (OSSL_PKEY_PARAM_RSA_TEST_XP2) <unsigned integer>
"xq1" (OSSL_PKEY_PARAM_RSA_TEST_XQ1) <unsigned integer>
"xq2" (OSSL_PKEY_PARAM_RSA_TEST_XQ2) <unsigned integer>
    These 4 fields are normally randomly generated. The prime factors "p1", "p2", "q1" and "q2" are determined from these values.

  RSA key parameters for FIPS module testing
The following intermediate values can be retrieved only if the values specified in "RSA key generation parameters for FIPS module testing" are set. These should not be accessed in a production environment.

"p1" (OSSL_PKEY_PARAM_RSA_TEST_P1) <unsigned integer>
"p2" (OSSL_PKEY_PARAM_RSA_TEST_P2) <unsigned integer>
"q1" (OSSL_PKEY_PARAM_RSA_TEST_Q1) <unsigned integer>
"q2" (OSSL_PKEY_PARAM_RSA_TEST_Q2) <unsigned integer>
    The auxiliary probable primes.

  RSA key validation
For RSA keys, EVP_PKEY_param_check(3) and EVP_PKEY_param_check_quick(3) both return 1 unconditionally.

For RSA keys, EVP_PKEY_public_check(3) conforms to the SP800-56Br1 public key check when the OpenSSL FIPS provider is used. The OpenSSL default provider performs similar tests but relaxes the keysize restrictions for backwards compatibility.

For RSA keys, EVP_PKEY_public_check_quick(3) is the same as EVP_PKEY_public_check(3).

For RSA keys, EVP_PKEY_private_check(3) conforms to the SP800-56Br1 private key test.

For RSA keys, EVP_PKEY_pairwise_check(3) conforms to the SP800-56Br1 KeyPair Validation check for the OpenSSL FIPS provider. The OpenSSL default provider allows testing of the validity of multi-primes.

CONFORMING TO

FIPS186-5
    Section A.1.6 Generation of Probable Primes with Conditions Based on Auxiliary Probable Primes

RFC 8017, excluding RSA-PSS and RSA-OAEP

EXAMPLES
An EVP_PKEY context can be obtained by calling:

    EVP_PKEY_CTX *pctx =
        EVP_PKEY_CTX_new_from_name(NULL, "RSA", NULL);

An RSA key can be generated simply like this:

    pkey = EVP_RSA_gen(4096);

or like this:

    EVP_PKEY *pkey = NULL;
    EVP_PKEY_CTX *pctx =
        EVP_PKEY_CTX_new_from_name(NULL, "RSA", NULL);

    EVP_PKEY_keygen_init(pctx);
    EVP_PKEY_generate(pctx, &pkey);
    EVP_PKEY_CTX_free(pctx);

An RSA key can be generated with key generation parameters:

    unsigned int primes = 3;
    unsigned int bits = 4096;
    OSSL_PARAM params[3];
    EVP_PKEY *pkey = NULL;
    EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_from_name(NULL, "RSA", NULL);

    EVP_PKEY_keygen_init(pctx);

    params[0] = OSSL_PARAM_construct_uint("bits", &bits);
    params[1] = OSSL_PARAM_construct_uint("primes", &primes);
    params[2] = OSSL_PARAM_construct_end();
    EVP_PKEY_CTX_set_params(pctx, params);

    EVP_PKEY_generate(pctx, &pkey);
    EVP_PKEY_print_private(bio_out, pkey, 0, NULL);
    EVP_PKEY_CTX_free(pctx);

SEE ALSO
EVP_RSA_gen(3), EVP_KEYMGMT(3), EVP_PKEY(3), provider-keymgmt(7)

HISTORY
The RSA key generation parameters "a" and "b" were added in OpenSSL 4.0.

COPYRIGHT
Copyright 2020-2024 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>.