1EVP_KDF-SS(7ossl)                   OpenSSL                  EVP_KDF-SS(7ossl)
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NAME

6       EVP_KDF-SS - The Single Step / One Step EVP_KDF implementation
7

DESCRIPTION

9       The EVP_KDF-SS algorithm implements the Single Step key derivation
10       function (SSKDF).  SSKDF derives a key using input such as a shared
11       secret key (that was generated during the execution of a key
12       establishment scheme) and fixedinfo.  SSKDF is also informally referred
13       to as 'Concat KDF'.
14
15   Auxiliary function
16       The implementation uses a selectable auxiliary function H, which can be
17       one of:
18
19       H(x) = hash(x, digest=md)
20       H(x) = HMAC_hash(x, key=salt, digest=md)
21       H(x) = KMACxxx(x, key=salt, custom="KDF", outlen=mac_size)
22
23       Both the HMAC and KMAC implementations set the key using the 'salt'
24       value.  The hash and HMAC also require the digest to be set.
25
26   Identity
27       "SSKDF" is the name for this implementation; it can be used with the
28       EVP_KDF_fetch() function.
29
30   Supported parameters
31       The supported parameters are:
32
33       "properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
34       "digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
35       "mac" (OSSL_KDF_PARAM_MAC) <UTF8 string>
36       "maclen" (OSSL_KDF_PARAM_MAC_SIZE) <unsigned integer>
37       "salt" (OSSL_KDF_PARAM_SALT) <octet string>
38           These parameters work as described in "PARAMETERS" in EVP_KDF(3).
39
40       "key" (EVP_KDF_CTRL_SET_KEY) <octet string>
41           This parameter set the shared secret that is used for key
42           derivation.
43
44       "info" (OSSL_KDF_PARAM_INFO) <octet string>
45           This parameter sets an optional value for fixedinfo, also known as
46           otherinfo.
47

NOTES

49       A context for SSKDF can be obtained by calling:
50
51        EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
52        EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
53
54       The output length of an SSKDF is specified via the keylen parameter to
55       the EVP_KDF_derive(3) function.
56

EXAMPLES

58       This example derives 10 bytes using H(x) = SHA-256, with the secret key
59       "secret" and fixedinfo value "label":
60
61        EVP_KDF *kdf;
62        EVP_KDF_CTX *kctx;
63        unsigned char out[10];
64        OSSL_PARAM params[4], *p = params;
65
66        kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
67        kctx = EVP_KDF_CTX_new(kdf);
68        EVP_KDF_free(kdf);
69
70        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
71                                                SN_sha256, strlen(SN_sha256));
72        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
73                                                 "secret", (size_t)6);
74        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
75                                                 "label", (size_t)5);
76        *p = OSSL_PARAM_construct_end();
77        if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
78            error("EVP_KDF_derive");
79        }
80
81        EVP_KDF_CTX_free(kctx);
82
83       This example derives 10 bytes using H(x) = HMAC(SHA-256), with the
84       secret key "secret", fixedinfo value "label" and salt "salt":
85
86        EVP_KDF *kdf;
87        EVP_KDF_CTX *kctx;
88        unsigned char out[10];
89        OSSL_PARAM params[6], *p = params;
90
91        kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
92        kctx = EVP_KDF_CTX_new(kdf);
93        EVP_KDF_free(kdf);
94
95        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
96                                                SN_hmac, strlen(SN_hmac));
97        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
98                                                SN_sha256, strlen(SN_sha256));
99        *p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
100                                                 "secret", (size_t)6);
101        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
102                                                 "label", (size_t)5);
103        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
104                                                 "salt", (size_t)4);
105        *p = OSSL_PARAM_construct_end();
106        if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
107            error("EVP_KDF_derive");
108        }
109
110        EVP_KDF_CTX_free(kctx);
111
112       This example derives 10 bytes using H(x) = KMAC128(x,salt,outlen), with
113       the secret key "secret" fixedinfo value "label", salt of "salt" and
114       KMAC outlen of 20:
115
116        EVP_KDF *kdf;
117        EVP_KDF_CTX *kctx;
118        unsigned char out[10];
119        OSSL_PARAM params[7], *p = params;
120
121        kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
122        kctx = EVP_KDF_CTX_new(kdf);
123        EVP_KDF_free(kdf);
124
125        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
126                                                SN_kmac128, strlen(SN_kmac128));
127        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
128                                                SN_sha256, strlen(SN_sha256));
129        *p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
130                                                 "secret", (size_t)6);
131        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
132                                                 "label", (size_t)5);
133        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
134                                                 "salt", (size_t)4);
135        *p++ = OSSL_PARAM_construct_size_t(OSSL_KDF_PARAM_MAC_SIZE, (size_t)20);
136        *p = OSSL_PARAM_construct_end();
137        if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
138            error("EVP_KDF_derive");
139        }
140
141        EVP_KDF_CTX_free(kctx);
142

CONFORMING TO

144       NIST SP800-56Cr1.
145

SEE ALSO

147       EVP_KDF(3), EVP_KDF_CTX_new(3), EVP_KDF_CTX_free(3),
148       EVP_KDF_CTX_set_params(3), EVP_KDF_CTX_get_kdf_size(3),
149       EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)
150

HISTORY

152       This functionality was added to OpenSSL 3.0.
153
155       Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.
156       Copyright (c) 2019, Oracle and/or its affiliates.  All rights reserved.
157
158       Licensed under the Apache License 2.0 (the "License").  You may not use
159       this file except in compliance with the License.  You can obtain a copy
160       in the file LICENSE in the source distribution or at
161       <https://www.openssl.org/source/license.html>.
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1653.0.5                             2022-07-05                 EVP_KDF-SS(7ossl)
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