{ "mode": "man", "parameter": "EVP_KDF-KB", "section": "7SSL", "url": "https://www.chedong.com/phpMan.php/man/EVP_KDF-KB/7SSL/json", "generated": "2026-10-06T04:07:55Z", "sections": { "NAME": { "content": "EVPKDF-KB - The Key-Based EVPKDF implementation\n", "subsections": [] }, "DESCRIPTION": { "content": "The EVPKDF-KB algorithm implements the Key-Based key derivation function (KBKDF). KBKDF\nderives a key from repeated application of a keyed MAC to an input secret (and other optional\nvalues).\n", "subsections": [ { "name": "Identity", "content": "\"KBKDF\" is the name for this implementation; it can be used with the EVPKDFfetch()\nfunction.\n" }, { "name": "Supported parameters", "content": "The supported parameters are:\n\n\"mode\" (OSSLKDFPARAMMODE) \nThe mode parameter determines which flavor of KBKDF to use - currently the choices are\n\"counter\" and \"feedback\". \"counter\" is the default, and will be used if unspecified.\n\n\"mac\" (OSSLKDFPARAMMAC) \nThe value is either CMAC or HMAC.\n\n\"digest\" (OSSLKDFPARAMDIGEST) \n\"cipher\" (OSSLKDFPARAMCIPHER) \n\"properties\" (OSSLKDFPARAMPROPERTIES) \n\"key\" (OSSLKDFPARAMKEY) \n\"salt\" (OSSLKDFPARAMSALT) \n\"info (OSSLKDFPARAMINFO) \n\"seed\" (OSSLKDFPARAMSEED) \nThe seed parameter is unused in counter mode.\n\n\"use-l\" (OSSLKDFPARAMKBKDFUSEL) \nSet to 0 to disable use of the optional Fixed Input data 'L' (see SP800-108). The\ndefault value of 1 will be used if unspecified.\n\n\"use-separator\" (OSSLKDFPARAMKBKDFUSESEPARATOR) \nSet to 0 to disable use of the optional Fixed Input data 'zero separator' (see SP800-108)\nthat is placed between the Label and Context. The default value of 1 will be used if\nunspecified.\n\nDepending on whether mac is CMAC or HMAC, either digest or cipher is required (respectively)\nand the other is unused.\n\nThe parameters key, salt, info, and seed correspond to KI, Label, Context, and IV\n(respectively) in SP800-108. As in that document, salt, info, and seed are optional and may\nbe omitted.\n\n\"mac\", \"digest\", cipher\" and \"properties\" are described in \"PARAMETERS\" in EVPKDF(3).\n" } ] }, "NOTES": { "content": "A context for KBKDF can be obtained by calling:\n\nEVPKDF *kdf = EVPKDFfetch(NULL, \"KBKDF\", NULL);\nEVPKDFCTX *kctx = EVPKDFCTXnew(kdf);\n\nThe output length of an KBKDF is specified via the \"keylen\" parameter to the\nEVPKDFderive(3) function.\n\nNote that currently OpenSSL only implements counter and feedback modes. Other variants may\nbe supported in the future.\n", "subsections": [] }, "EXAMPLES": { "content": "This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI \"secret\", Label \"label\", and\nContext \"context\".\n\nEVPKDF *kdf;\nEVPKDFCTX *kctx;\nunsigned char out[10];\nOSSLPARAM params[6], *p = params;\n\nkdf = EVPKDFfetch(NULL, \"KBKDF\", NULL);\nkctx = EVPKDFCTXnew(kdf);\nEVPKDFfree(kdf);\n\n*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMDIGEST,\n\"SHA2-256\", 0);\n*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMMAC,\n\"HMAC\", 0);\n*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMKEY,\n\"secret\", strlen(\"secret\"));\n*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMSALT,\n\"label\", strlen(\"label\"));\n*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMINFO,\n\"context\", strlen(\"context\"));\n*p = OSSLPARAMconstructend();\nif (EVPKDFderive(kctx, out, sizeof(out), params) <= 0)\nerror(\"EVPKDFderive\");\n\nEVPKDFCTXfree(kctx);\n\nThis example derives 10 bytes using FEEDBACK-CMAC-AES256, with KI \"secret\", Label \"label\",\nand IV \"sixteen bytes iv\".\n\nEVPKDF *kdf;\nEVPKDFCTX *kctx;\nunsigned char out[10];\nOSSLPARAM params[8], *p = params;\nunsigned char *iv = \"sixteen bytes iv\";\n\nkdf = EVPKDFfetch(NULL, \"KBKDF\", NULL);\nkctx = EVPKDFCTXnew(kdf);\nEVPKDFfree(kdf);\n\n*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMCIPHER, \"AES256\", 0);\n*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMMAC, \"CMAC\", 0);\n*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMMODE, \"FEEDBACK\", 0);\n*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMKEY,\n\"secret\", strlen(\"secret\"));\n*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMSALT,\n\"label\", strlen(\"label\"));\n*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMINFO,\n\"context\", strlen(\"context\"));\n*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMSEED,\niv, strlen(iv));\n*p = OSSLPARAMconstructend();\nif (EVPKDFderive(kctx, out, sizeof(out), params) <= 0)\nerror(\"EVPKDFderive\");\n\nEVPKDFCTXfree(kctx);\n", "subsections": [] }, "CONFORMING TO": { "content": "NIST SP800-108, IETF RFC 6803, IETF RFC 8009.\n", "subsections": [] }, "SEE ALSO": { "content": "EVPKDF(3), EVPKDFCTXfree(3), EVPKDFCTXgetkdfsize(3), EVPKDFderive(3), \"PARAMETERS\"\nin EVPKDF(3)\n", "subsections": [] }, "HISTORY": { "content": "This functionality was added in OpenSSL 3.0.\n", "subsections": [] }, "COPYRIGHT": { "content": "Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved. Copyright 2019 Red\nHat, Inc.\n\nLicensed under the Apache License 2.0 (the \"License\"). You may not use this file except in\ncompliance with the License. You can obtain a copy in the file LICENSE in the source\ndistribution or at .\n\n3.0.13 2026-07-29 EVPKDF-KB(7SSL)", "subsections": [] } }, "summary": "EVPKDF-KB - The Key-Based EVPKDF implementation", "flags": [], "examples": [ "This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI \"secret\", Label \"label\", and", "Context \"context\".", "EVPKDF *kdf;", "EVPKDFCTX *kctx;", "unsigned char out[10];", "OSSLPARAM params[6], *p = params;", "kdf = EVPKDFfetch(NULL, \"KBKDF\", NULL);", "kctx = EVPKDFCTXnew(kdf);", "EVPKDFfree(kdf);", "*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMDIGEST,", "\"SHA2-256\", 0);", "*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMMAC,", "\"HMAC\", 0);", "*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMKEY,", "\"secret\", strlen(\"secret\"));", "*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMSALT,", "\"label\", strlen(\"label\"));", "*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMINFO,", "\"context\", strlen(\"context\"));", "*p = OSSLPARAMconstructend();", "if (EVPKDFderive(kctx, out, sizeof(out), params) <= 0)", "error(\"EVPKDFderive\");", "EVPKDFCTXfree(kctx);", "This example derives 10 bytes using FEEDBACK-CMAC-AES256, with KI \"secret\", Label \"label\",", "and IV \"sixteen bytes iv\".", "EVPKDF *kdf;", "EVPKDFCTX *kctx;", "unsigned char out[10];", "OSSLPARAM params[8], *p = params;", "unsigned char *iv = \"sixteen bytes iv\";", "kdf = EVPKDFfetch(NULL, \"KBKDF\", NULL);", "kctx = EVPKDFCTXnew(kdf);", "EVPKDFfree(kdf);", "*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMCIPHER, \"AES256\", 0);", "*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMMAC, \"CMAC\", 0);", "*p++ = OSSLPARAMconstructutf8string(OSSLKDFPARAMMODE, \"FEEDBACK\", 0);", "*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMKEY,", "\"secret\", strlen(\"secret\"));", "*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMSALT,", "\"label\", strlen(\"label\"));", "*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMINFO,", "\"context\", strlen(\"context\"));", "*p++ = OSSLPARAMconstructoctetstring(OSSLKDFPARAMSEED,", "iv, strlen(iv));", "*p = OSSLPARAMconstructend();", "if (EVPKDFderive(kctx, out, sizeof(out), params) <= 0)", "error(\"EVPKDFderive\");", "EVPKDFCTXfree(kctx);" ], "see_also": [ { "name": "EVPKDF", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/EVPKDF/3/json" }, { "name": "EVPKDFCTXfree", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/EVPKDFCTXfree/3/json" }, { "name": "EVPKDFCTXgetkdfsize", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/EVPKDFCTXgetkdfsize/3/json" }, { "name": "EVPKDFderive", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/EVPKDFderive/3/json" }, { "name": "EVPKDF", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/EVPKDF/3/json" } ] }