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1 .\" -*- mode: troff; coding: utf-8 -*-
57 .IX Title "EVP_KDF-HKDF 7ossl"
58 .TH EVP_KDF-HKDF 7ossl 2025-09-30 3.5.4 OpenSSL
64 EVP_KDF\-HKDF \- The HKDF EVP_KDF implementation
69 The EVP_KDF\-HKDF algorithm implements the HKDF key derivation function.
70 HKDF follows the "extract-then-expand" paradigm, where the KDF logically
72 and "extracts" from it a fixed-length pseudorandom key K. The second stage
100 .IP """mode"" (\fBOSSL_KDF_PARAM_MODE\fR) <UTF8 string> or <integer>" 4
101 .IX Item """mode"" (OSSL_KDF_PARAM_MODE) <UTF8 string> or <integer>"
102 This parameter sets the mode for the HKDF operation.
107 This is the default mode.  Calling \fBEVP_KDF_derive\fR\|(3) on an EVP_KDF_CTX set
110 intermediate fixed-length pseudorandom key K is not returned.
112 In this mode the digest, key, salt and info values must be set before a key is
116 In this mode calling \fBEVP_KDF_derive\fR\|(3) will just perform the extract
117 operation. The value returned will be the intermediate fixed-length pseudorandom
119 up by calling \fBEVP_KDF_CTX_get_kdf_size()\fR after setting the mode and digest.
125 In this mode calling \fBEVP_KDF_derive\fR\|(3) will just perform the expand
126 operation. The input key should be set to the intermediate fixed-length
136 .IP """fips-indicator"" (\fBOSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR\fR) <integer>" 4
137 .IX Item """fips-indicator"" (OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR) <integer>"
139 This may be used after calling EVP_KDF_derive. It returns 0 if "key-check"
141 .IP """key-check"" (\fBOSSL_KDF_PARAM_FIPS_KEY_CHECK\fR) <integer>" 4
142 .IX Item """key-check"" (OSSL_KDF_PARAM_FIPS_KEY_CHECK) <integer>"
144 length of used key-derivation key (\fBOSSL_KDF_PARAM_KEY\fR) is shorter than 112
147 "fips-indicator" to 0.
148 This option breaks FIPS compliance if it causes the approved "fips-indicator"
162 the intermediate fixed-length pseudorandom key otherwise an error will occur.
163 For that mode, the fixed output size can be looked up by calling \fBEVP_KDF_CTX_get_kdf_size()\fR
164 after setting the mode and digest on the \fBEVP_KDF_CTX\fR.
167 This example derives 10 bytes using SHA\-256 with the secret key "secret",
207 \&\fBEVP_KDF\-TLS13_KDF\fR\|(7)
213 Copyright 2016\-2024 The OpenSSL Project Authors. All Rights Reserved.