1 /* 2 * Copyright 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef SYSTEM_KEYMASTER_HKDF_H_ 18 #define SYSTEM_KEYMASTER_HKDF_H_ 19 20 #include <hardware/keymaster_defs.h> 21 #include <keymaster/serializable.h> 22 23 #include <UniquePtr.h> 24 25 namespace keymaster { 26 27 // Rfc5869HmacSha256Kdf implements the key derivation function specified in RFC 5869 (using 28 // SHA256) and outputs key material, as needed by ECIES. 29 // See https://tools.ietf.org/html/rfc5869 for details. 30 class Rfc5869HmacSha256Kdf { 31 public: 32 // |secret|: the input shared secret (or, from RFC 5869, the IKM). 33 // |salt|: an (optional) public salt / non-secret random value. While 34 // optional, callers are strongly recommended to provide a salt. There is no 35 // added security value in making this larger than the SHA-256 block size of 36 // 64 bytes. 37 // |info|: an (optional) label to distinguish different uses of HKDF. It is 38 // optional context and application specific information (can be a zero-length 39 // string). 40 // |key_bytes_to_generate|: the number of bytes of key material to generate. 41 Rfc5869HmacSha256Kdf(Buffer& secret, Buffer& salt, Buffer& info, size_t key_bytes_to_generate, 42 keymaster_error_t* error); 43 44 Rfc5869HmacSha256Kdf(const uint8_t* secret, size_t secret_len, const uint8_t* salt, 45 size_t salt_len, const uint8_t* info, size_t info_len, 46 size_t key_bytes_to_generate, keymaster_error_t* error); 47 secret_key(Buffer * buf)48 bool secret_key(Buffer* buf) const { 49 return buf->Reinitialize(secret_key_.get(), secret_key_len_); 50 }; 51 52 private: 53 UniquePtr<uint8_t[]> output_; 54 UniquePtr<uint8_t[]> secret_key_; 55 size_t secret_key_len_; 56 }; 57 58 } // namespace keymaster 59 60 #endif // SYSTEM_KEYMASTER_HKDF_H_ 61