mirror of https://github.com/openssl/openssl
116 lines
3.3 KiB
Plaintext
116 lines
3.3 KiB
Plaintext
=pod
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=head1 NAME
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EVP_KDF-KRB5KDF - The RFC3961 Krb5 KDF EVP_KDF implementation
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=head1 DESCRIPTION
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Support for computing the B<KRB5KDF> KDF through the B<EVP_KDF> API.
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The EVP_KDF-KRB5KDF algorithm implements the key derivation function defined
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in RFC 3961, section 5.1 and is used by Krb5 to derive session keys.
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Three inputs are required to perform key derivation: a cipher, (for example
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AES-128-CBC), the initial key, and a constant.
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=head2 Identity
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"KRB5KDF" is the name for this implementation;
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it can be used with the EVP_KDF_fetch() function.
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=head2 Supported parameters
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The supported parameters are:
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=over 4
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=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
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=item "cipher" (B<OSSL_KDF_PARAM_CIPHER>) <UTF8 string>
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=item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string>
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These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
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=item "constant" (B<OSSL_KDF_PARAM_CONSTANT>) <octet string>
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This parameter sets the constant value for the KDF.
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If a value is already set, the contents are replaced.
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=back
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=head1 NOTES
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A context for KRB5KDF can be obtained by calling:
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EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
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EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
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The output length of the KRB5KDF derivation is specified via the I<keylen>
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parameter to the L<EVP_KDF_derive(3)> function, and MUST match the key
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length for the chosen cipher or an error is returned. Moreover, the
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constant's length must not exceed the block size of the cipher.
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Since the KRB5KDF output length depends on the chosen cipher, calling
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L<EVP_KDF_CTX_get_kdf_size(3)> to obtain the requisite length returns the correct length
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only after the cipher is set. Prior to that B<EVP_MAX_KEY_LENGTH> is returned.
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The caller must allocate a buffer of the correct length for the chosen
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cipher, and pass that buffer to the L<EVP_KDF_derive(3)> function along
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with that length.
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=head1 EXAMPLES
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This example derives a key using the AES-128-CBC cipher:
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EVP_KDF *kdf;
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EVP_KDF_CTX *kctx;
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unsigned char key[16] = "01234...";
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unsigned char constant[] = "I'm a constant";
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unsigned char out[16];
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size_t outlen = sizeof(out);
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OSSL_PARAM params[4], *p = params;
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kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
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kctx = EVP_KDF_CTX_new(kdf);
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EVP_KDF_free(kdf);
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*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER,
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SN_aes_128_cbc,
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strlen(SN_aes_128_cbc));
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*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
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key, (size_t)16);
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*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_CONSTANT,
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constant, strlen(constant));
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*p = OSSL_PARAM_construct_end();
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if (EVP_KDF_derive(kctx, out, outlen, params) <= 0)
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/* Error */
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EVP_KDF_CTX_free(kctx);
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=head1 CONFORMING TO
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RFC 3961
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=head1 SEE ALSO
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L<EVP_KDF(3)>,
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L<EVP_KDF_CTX_free(3)>,
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L<EVP_KDF_CTX_get_kdf_size(3)>,
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L<EVP_KDF_derive(3)>,
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L<EVP_KDF(3)/PARAMETERS>
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=head1 HISTORY
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This functionality was added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2016-2021 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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