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      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_ISO18033KDF_H_
     18 #define SYSTEM_KEYMASTER_ISO18033KDF_H_
     19 
     20 #include <keymaster/km_openssl/kdf.h>
     21 
     22 #include <hardware/keymaster_defs.h>
     23 
     24 #include <keymaster/serializable.h>
     25 #include <keymaster/UniquePtr.h>
     26 
     27 namespace keymaster {
     28 
     29 /**
     30  * A light implementation of ISO18033KDF as defined by ISO-18033-2 (www.shoup.net/iso/std6.pdf) and
     31  * its slightly different variant ANSI-X9-42.
     32  */
     33 class Iso18033Kdf : public Kdf {
     34   public:
     35     ~Iso18033Kdf() {}
     36 
     37     bool Init(keymaster_digest_t digest_type, const uint8_t* secret, size_t secret_len) {
     38         return Kdf::Init(digest_type, secret, secret_len, nullptr /* salt */, 0 /* salt_len */);
     39     }
     40 
     41     /**
     42      * Generates ISO18033's derived key, as defined in ISO-18033-2 and ANSI-X9-42. In ISO 18033-2,
     43      * KDF takes a secret and outputs:
     44      *
     45      * hash(secret || start_counter) || hash(secret|| start_counter + 1) || ...
     46      *
     47      * In ANSI-X9-42, KDF takes a secret and additional info, and outputs:
     48      *
     49      * hash(secret || start_counter || info) || hash(secret || start_counter + 1 || info) || ...
     50      *
     51      * Note that the KDFs are the same if the info field is considered optional.  In both cases the
     52      * length of the output is specified by the caller, and the counter is encoded as a 4-element
     53      * byte array.
     54      */
     55     bool GenerateKey(const uint8_t* info, size_t info_len, uint8_t* output,
     56                      size_t output_len) override;
     57 
     58   protected:
     59     explicit Iso18033Kdf(uint32_t start_counter) : start_counter_(start_counter) {}
     60 
     61   private:
     62     uint32_t start_counter_;
     63 };
     64 
     65 }  // namespace keymaster
     66 
     67 #endif  // SYSTEM_KEYMASTER_ISO18033KDF_H_
     68