1EVP_KDF-TLS13_KDF(7ossl) OpenSSL EVP_KDF-TLS13_KDF(7ossl)
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6 EVP_KDF-TLS13_KDF - The TLS 1.3 EVP_KDF implementation
7
9 Support for computing the TLS 1.3 version of the HKDF KDF through the
10 EVP_KDF API.
11 The EVP_KDF-TLS13_KDF algorithm implements the HKDF key derivation
13 function as used by TLS 1.3.
14 Identity
16 "TLS13-KDF" is the name for this implementation; it can be used with
17 the EVP_KDF_fetch() function.
18 Supported parameters
20 The supported parameters are:
21 "properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
23 "digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
24 "key" (OSSL_KDF_PARAM_KEY) <octet string>
25 "salt" (OSSL_KDF_PARAM_SALT) <octet string>
26 These parameters work as described in "PARAMETERS" in EVP_KDF(3).
27 "prefix" (OSSL_KDF_PARAM_PREFIX) <octet string>
29 This parameter sets the label prefix on the specified TLS 1.3 KDF
30 context. For TLS 1.3 this should be set to the ASCII string "tls13
31 " without a trailing zero byte. Refer to RFC 8446 section 7.1 "Key
32 Schedule" for details.
33 "label" (OSSL_KDF_PARAM_LABEL) <octet string>
35 This parameter sets the label on the specified TLS 1.3 KDF context.
36 Refer to RFC 8446 section 7.1 "Key Schedule" for details.
37 "data" (OSSL_KDF_PARAM_DATA) <octet string>
39 This parameter sets the context data on the specified TLS 1.3 KDF
40 context. Refer to RFC 8446 section 7.1 "Key Schedule" for details.
41 "mode" (OSSL_KDF_PARAM_MODE) <UTF8 string> or <integer>
43 This parameter sets the mode for the TLS 1.3 KDF operation. There
44 are two modes that are currently defined:
45 "EXTRACT_ONLY" or EVP_KDF_HKDF_MODE_EXTRACT_ONLY
47 In this mode calling EVP_KDF_derive(3) will just perform the
48 extract operation. The value returned will be the intermediate
49 fixed-length pseudorandom key K. The keylen parameter must
50 match the size of K, which can be looked up by calling
51 EVP_KDF_CTX_get_kdf_size() after setting the mode and digest.
52 The digest, key and salt values must be set before a key is
54 derived otherwise an error will occur.
55 "EXPAND_ONLY" or EVP_KDF_HKDF_MODE_EXPAND_ONLY
57 In this mode calling EVP_KDF_derive(3) will just perform the
58 expand operation. The input key should be set to the
59 intermediate fixed-length pseudorandom key K returned from a
60 previous extract operation.
61 The digest, key and info values must be set before a key is
63 derived otherwise an error will occur.
64
66 This KDF is intended for use by the TLS 1.3 implementation in libssl.
67 It does not support all the options and capabilities that HKDF does.
68 The OSSL_PARAM array passed to EVP_KDF_derive(3) or
70 EVP_KDF_CTX_set_params(3) must specify all of the parameters required.
71 This KDF does not support a piecemeal approach to providing these.
72 A context for a TLS 1.3 KDF can be obtained by calling:
74 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "TLS13-KDF", NULL);
76 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
77 The output length of a TLS 1.3 KDF expand operation is specified via
79 the keylen parameter to the EVP_KDF_derive(3) function. When using
80 EVP_KDF_HKDF_MODE_EXTRACT_ONLY the keylen parameter must equal the size
81 of the intermediate fixed-length pseudorandom key otherwise an error
82 will occur. For that mode, the fixed output size can be looked up by
83 calling EVP_KDF_CTX_get_kdf_size() after setting the mode and digest on
84 the EVP_KDF_CTX.
85
87 RFC 8446
88
90 EVP_KDF(3), EVP_KDF_CTX_new(3), EVP_KDF_CTX_free(3),
91 EVP_KDF_CTX_get_kdf_size(3), EVP_KDF_CTX_set_params(3),
92 EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3), EVP_KDF-HKDF(7)
93
95 Copyright 2021 The OpenSSL Project Authors. All Rights Reserved.
96 Licensed under the Apache License 2.0 (the "License"). You may not use
98 this file except in compliance with the License. You can obtain a copy
99 in the file LICENSE in the source distribution or at
100 <https://www.openssl.org/source/license.html>.
1013.0.5 2022-11-01 EVP_KDF-TLS13_KDF(7ossl)