| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | EVP_RAND-SEED-SRC - The randomness seed source EVP_RAND implementation
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| 6 |
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| 7 | =head1 DESCRIPTION
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| 8 |
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| 9 | Support for deterministic random number generator seeding through the
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| 10 | B<EVP_RAND> API.
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| 11 |
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| 12 | The seed sources used are specified at the time OpenSSL is configured for
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| 13 | building using the B<--with-rand-seed=> option. By default, operating system
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| 14 | randomness sources are used.
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| 15 |
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| 16 | =head2 Identity
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| 17 |
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| 18 | "SEED-SRC" is the name for this implementation; it can be used with the
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| 19 | EVP_RAND_fetch() function.
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| 20 |
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| 21 | =head2 Supported parameters
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| 22 |
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| 23 | The supported parameters are:
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| 24 |
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| 25 | =over 4
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| 26 |
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| 27 | =item "state" (B<OSSL_RAND_PARAM_STATE>) <integer>
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| 28 |
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| 29 | =item "strength" (B<OSSL_RAND_PARAM_STRENGTH>) <unsigned integer>
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| 30 |
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| 31 | =item "max_request" (B<OSSL_RAND_PARAM_MAX_REQUEST>) <unsigned integer>
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| 32 |
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| 33 | These parameters work as described in L<EVP_RAND(3)/PARAMETERS>.
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| 34 |
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| 35 | =back
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| 36 |
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| 37 | =head1 NOTES
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| 38 |
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| 39 | A context for the seed source can be obtained by calling:
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| 40 |
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| 41 | EVP_RAND *rand = EVP_RAND_fetch(NULL, "SEED-SRC", NULL);
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| 42 | EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand);
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| 43 |
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| 44 | =head1 EXAMPLES
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| 45 |
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| 46 | EVP_RAND *rand;
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| 47 | EVP_RAND_CTX *seed, *rctx;
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| 48 | unsigned char bytes[100];
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| 49 | OSSL_PARAM params[2], *p = params;
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| 50 | unsigned int strength = 128;
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| 51 |
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| 52 | /* Create a seed source */
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| 53 | rand = EVP_RAND_fetch(NULL, "SEED-SRC", NULL);
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| 54 | seed = EVP_RAND_CTX_new(rand, NULL);
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| 55 | EVP_RAND_free(rand);
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| 56 |
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| 57 | /* Feed this into a DRBG */
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| 58 | rand = EVP_RAND_fetch(NULL, "CTR-DRBG", NULL);
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| 59 | rctx = EVP_RAND_CTX_new(rand, seed);
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| 60 | EVP_RAND_free(rand);
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| 61 |
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| 62 | /* Configure the DRBG */
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| 63 | *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_CIPHER,
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| 64 | SN_aes_256_ctr, 0);
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| 65 | *p = OSSL_PARAM_construct_end();
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| 66 | EVP_RAND_instantiate(rctx, strength, 0, NULL, 0, params);
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| 67 |
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| 68 | EVP_RAND_generate(rctx, bytes, sizeof(bytes), strength, 0, NULL, 0);
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| 69 |
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| 70 | EVP_RAND_CTX_free(rctx);
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| 71 | EVP_RAND_CTX_free(seed);
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| 72 |
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| 73 | =head1 SEE ALSO
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| 74 |
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| 75 | L<EVP_RAND(3)>,
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| 76 | L<EVP_RAND(3)/PARAMETERS>
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| 77 |
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| 78 | =head1 COPYRIGHT
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| 79 |
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| 80 | Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.
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| 81 |
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| 82 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 83 | this file except in compliance with the License. You can obtain a copy
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| 84 | in the file LICENSE in the source distribution or at
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| 85 | L<https://www.openssl.org/source/license.html>.
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| 86 |
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| 87 | =cut
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