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EVP_KDF_SS(7)                       OpenSSL                      EVP_KDF_SS(7)
NAME
       EVP_KDF_SS - The Single Step / One Step EVP_KDF implementation
DESCRIPTION
       The EVP_KDF_SS algorithm implements the Single Step key derivation
       function (SSKDF).  SSKDF derives a key using input such as a shared
       secret key (that was generated during the execution of a key
       establishment scheme) and fixedinfo.  SSKDF is also informally referred
       to as 'Concat KDF'.
   Auxilary function
       The implementation uses a selectable auxiliary function H, which can be
       in the backported version only a:
       H(x) = hash(x, digest=md)
   Numeric identity
       EVP_KDF_SS is the numeric identity for this implementation; it can be
       used with the EVP_KDF_CTX_new_id() function.
   Supported controls
       The supported controls are:
       EVP_KDF_CTRL_SET_MD
           This control works as described in "CONTROLS" in EVP_KDF_CTX(3).
       EVP_KDF_CTRL_SET_KEY
           This control expects two arguments: "unsigned char *secret",
           "size_t secretlen"
           The shared secret used for key derivation.  This control sets the
           secret.
           EVP_KDF_ctrl_str() takes two type strings for this control:
           "secret"
               The value string is used as is.
           "hexsecret"
               The value string is expected to be a hexadecimal number, which
               will be decoded before being passed on as the control value.
       EVP_KDF_CTRL_SET_SSKDF_INFO
           This control expects two arguments: "unsigned char *info", "size_t
           infolen"
           An optional value for fixedinfo, also known as otherinfo. This
           control sets the fixedinfo.
           EVP_KDF_ctrl_str() takes two type strings for this control:
           "info"
               The value string is used as is.
           "hexinfo"
               The value string is expected to be a hexadecimal number, which
               will be decoded before being passed on as the control value.
NOTES
       A context for SSKDF can be obtained by calling:
       EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
       The output length of an SSKDF is specified via the "keylen" parameter
       to the EVP_KDF_derive(3) function.
EXAMPLE
       This example derives 10 bytes using H(x) = SHA-256, with the secret key
       "secret" and fixedinfo value "label":
         EVP_KDF_CTX *kctx;
         unsigned char out[10];
         kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
         if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
             error("EVP_KDF_CTRL_SET_MD");
         }
         if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
             error("EVP_KDF_CTRL_SET_KEY");
         }
         if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SSKDF_INFO, "label", (size_t)5) <= 0) {
             error("EVP_KDF_CTRL_SET_SSKDF_INFO");
         }
         if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
             error("EVP_KDF_derive");
         }
         EVP_KDF_CTX_free(kctx);
CONFORMING TO
       NIST SP800-56Cr1.
SEE ALSO
       EVP_KDF_CTX, EVP_KDF_CTX_new_id(3), EVP_KDF_CTX_free(3),
       EVP_KDF_ctrl(3), EVP_KDF_size(3), EVP_KDF_derive(3), "CONTROLS" in
       EVP_KDF_CTX(3)
HISTORY
       This functionality was added to OpenSSL 3.0.0.
COPYRIGHT
       Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
       Copyright (c) 2019, Oracle and/or its affiliates.  All rights reserved.
       Licensed under the Apache License 2.0 (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>;.
1.1.1k                            2024-10-09                     EVP_KDF_SS(7)