/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.codec.digest;
  
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Arrays;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import org.apache.commons.codec.Charsets;
  
  /**
   * SHA2-based Unix crypt implementation.
   * <p>
   * Based on the C implementation released into the Public Domain by Ulrich Drepper &lt;drepper@redhat.com&gt;
   * http://www.akkadia.org/drepper/SHA-crypt.txt
   * <p>
   * Conversion to Kotlin and from there to Java in 2012 by Christian Hammers &lt;ch@lathspell.de&gt; and likewise put
   * into the Public Domain.
   * <p>
   * This class is immutable and thread-safe.
   *
   * @version $Id: Sha2Crypt.html 889935 2013-12-11 05:05:13Z ggregory $
   * @since 1.7
   */
  public class Sha2Crypt {
  
      /** Default number of rounds if not explicitly specified. */
      private static final int ROUNDS_DEFAULT = 5000;
  
      /** Maximum number of rounds. */
      private static final int ROUNDS_MAX = 999999999;
  
      /** Minimum number of rounds. */
      private static final int ROUNDS_MIN = 1000;
  
      /** Prefix for optional rounds specification. */
      private static final String ROUNDS_PREFIX = "rounds=";
  
      /** The number of bytes the final hash value will have (SHA-256 variant). */
      private static final int SHA256_BLOCKSIZE = 32;
  
      /** The prefixes that can be used to identify this crypt() variant (SHA-256). */
      static final String SHA256_PREFIX = "$5$";
  
      /** The number of bytes the final hash value will have (SHA-512 variant). */
      private static final int SHA512_BLOCKSIZE = 64;
  
      /** The prefixes that can be used to identify this crypt() variant (SHA-512). */
      static final String SHA512_PREFIX = "$6$";
  
      /** The pattern to match valid salt values. */
      private static final Pattern SALT_PATTERN = Pattern
              .compile("^\\$([56])\\$(rounds=(\\d+)\\$)?([\\.\\/a-zA-Z0-9]{1,16}).*");
  
      /**
       * Generates a libc crypt() compatible "$5$" hash value with random salt.
       * <p>
       * See {@link Crypt#crypt(String, String)} for details.
       *
       * @throws RuntimeException
       *             when a {@link java.security.NoSuchAlgorithmException} is caught.
       */
      public static String sha256Crypt(byte[] keyBytes) {
          return sha256Crypt(keyBytes, null);
      }
  
      /**
       * Generates a libc6 crypt() compatible "$5$" hash value.
       * <p>
       * See {@link Crypt#crypt(String, String)} for details.
       *
       * @throws IllegalArgumentException
       *             if the salt does not match the allowed pattern
       * @throws RuntimeException
       *             when a {@link java.security.NoSuchAlgorithmException} is caught.
       */
      public static String sha256Crypt(byte[] keyBytes, String salt) {
          if (salt == null) {
              salt = SHA256_PREFIX + B64.getRandomSalt(8);
          }
          return sha2Crypt(keyBytes, salt, SHA256_PREFIX, SHA256_BLOCKSIZE, MessageDigestAlgorithms.SHA_256);
      }
  
     /**
      * Generates a libc6 crypt() compatible "$5$" or "$6$" SHA2 based hash value.
      * <p>
      * This is a nearly line by line conversion of the original C function. The numbered comments are from the
      * algorithm description, the short C-style ones from the original C code and the ones with "Remark" from me.
      * <p>
      * See {@link Crypt#crypt(String, String)} for details.
      *
      * @param keyBytes
      *            plaintext that should be hashed
      * @param salt
      *            real salt value without prefix or "rounds="
      * @param saltPrefix
      *            either $5$ or $6$
      * @param blocksize
      *            a value that differs between $5$ and $6$
      * @param algorithm
      *            {@link MessageDigest} algorithm identifier string
      * @return complete hash value including prefix and salt
      * @throws IllegalArgumentException
      *             if the given salt is {@code null} or does not match the allowed pattern
      * @throws IllegalArgumentException
      *             when a {@link NoSuchAlgorithmException} is caught
      * @see MessageDigestAlgorithms
      */
     private static String sha2Crypt(byte[] keyBytes, String salt, String saltPrefix, int blocksize, String algorithm) {
 
         int keyLen = keyBytes.length;
 
         // Extracts effective salt and the number of rounds from the given salt.
         int rounds = ROUNDS_DEFAULT;
         boolean roundsCustom = false;
         if (salt == null) {
             throw new IllegalArgumentException("Salt must not be null");
         }
 
         Matcher m = SALT_PATTERN.matcher(salt);
         if (m == null || !m.find()) {
             throw new IllegalArgumentException("Invalid salt value: " + salt);
         }
         if (m.group(3) != null) {
             rounds = Integer.parseInt(m.group(3));
             rounds = Math.max(ROUNDS_MIN, Math.min(ROUNDS_MAX, rounds));
             roundsCustom = true;
         }
         String saltString = m.group(4);
         byte[] saltBytes = saltString.getBytes(Charsets.UTF_8);
         int saltLen = saltBytes.length;
 
         // 1. start digest A
         // Prepare for the real work.
         MessageDigest ctx = DigestUtils.getDigest(algorithm);
 
         // 2. the password string is added to digest A
         /*
          * Add the key string.
          */
         ctx.update(keyBytes);
 
         // 3. the salt string is added to digest A. This is just the salt string
         // itself without the enclosing '$', without the magic salt_prefix $5$ and
         // $6$ respectively and without the rounds=<N> specification.
         //
         // NB: the MD5 algorithm did add the $1$ salt_prefix. This is not deemed
         // necessary since it is a constant string and does not add security
         // and /possibly/ allows a plain text attack. Since the rounds=<N>
         // specification should never be added this would also create an
         // inconsistency.
         /*
          * The last part is the salt string. This must be at most 16 characters and it ends at the first `$' character
          * (for compatibility with existing implementations).
          */
         ctx.update(saltBytes);
 
         // 4. start digest B
         /*
          * Compute alternate sha512 sum with input KEY, SALT, and KEY. The final result will be added to the first
          * context.
          */
         MessageDigest altCtx = DigestUtils.getDigest(algorithm);
 
         // 5. add the password to digest B
         /*
          * Add key.
          */
         altCtx.update(keyBytes);
 
         // 6. add the salt string to digest B
         /*
          * Add salt.
          */
         altCtx.update(saltBytes);
 
         // 7. add the password again to digest B
         /*
          * Add key again.
          */
         altCtx.update(keyBytes);
 
         // 8. finish digest B
         /*
          * Now get result of this (32 bytes) and add it to the other context.
          */
         byte[] altResult = altCtx.digest();
 
         // 9. For each block of 32 or 64 bytes in the password string (excluding
         // the terminating NUL in the C representation), add digest B to digest A
         /*
          * Add for any character in the key one byte of the alternate sum.
          */
         /*
          * (Remark: the C code comment seems wrong for key length > 32!)
          */
         int cnt = keyBytes.length;
         while (cnt > blocksize) {
             ctx.update(altResult, 0, blocksize);
             cnt -= blocksize;
         }
 
         // 10. For the remaining N bytes of the password string add the first
         // N bytes of digest B to digest A
         ctx.update(altResult, 0, cnt);
 
         // 11. For each bit of the binary representation of the length of the
         // password string up to and including the highest 1-digit, starting
         // from to lowest bit position (numeric value 1):
         //
         // a) for a 1-digit add digest B to digest A
         //
         // b) for a 0-digit add the password string
         //
         // NB: this step differs significantly from the MD5 algorithm. It
         // adds more randomness.
         /*
          * Take the binary representation of the length of the key and for every 1 add the alternate sum, for every 0
          * the key.
          */
         cnt = keyBytes.length;
         while (cnt > 0) {
             if ((cnt & 1) != 0) {
                 ctx.update(altResult, 0, blocksize);
             } else {
                 ctx.update(keyBytes);
             }
             cnt >>= 1;
         }
 
         // 12. finish digest A
         /*
          * Create intermediate result.
          */
         altResult = ctx.digest();
 
         // 13. start digest DP
         /*
          * Start computation of P byte sequence.
          */
         altCtx = DigestUtils.getDigest(algorithm);
 
         // 14. for every byte in the password (excluding the terminating NUL byte
         // in the C representation of the string)
         //
         // add the password to digest DP
         /*
          * For every character in the password add the entire password.
          */
         for (int i = 1; i <= keyLen; i++) {
             altCtx.update(keyBytes);
         }
 
         // 15. finish digest DP
         /*
          * Finish the digest.
          */
         byte[] tempResult = altCtx.digest();
 
         // 16. produce byte sequence P of the same length as the password where
         //
         // a) for each block of 32 or 64 bytes of length of the password string
         // the entire digest DP is used
         //
         // b) for the remaining N (up to 31 or 63) bytes use the first N
         // bytes of digest DP
         /*
          * Create byte sequence P.
          */
         byte[] pBytes = new byte[keyLen];
         int cp = 0;
         while (cp < keyLen - blocksize) {
             System.arraycopy(tempResult, 0, pBytes, cp, blocksize);
             cp += blocksize;
         }
         System.arraycopy(tempResult, 0, pBytes, cp, keyLen - cp);
 
         // 17. start digest DS
         /*
          * Start computation of S byte sequence.
          */
         altCtx = DigestUtils.getDigest(algorithm);
 
         // 18. repeast the following 16+A[0] times, where A[0] represents the first
         // byte in digest A interpreted as an 8-bit unsigned value
         //
         // add the salt to digest DS
         /*
          * For every character in the password add the entire password.
          */
         for (int i = 1; i <= 16 + (altResult[0] & 0xff); i++) {
             altCtx.update(saltBytes);
         }
 
         // 19. finish digest DS
         /*
          * Finish the digest.
          */
         tempResult = altCtx.digest();
 
         // 20. produce byte sequence S of the same length as the salt string where
         //
         // a) for each block of 32 or 64 bytes of length of the salt string
         // the entire digest DS is used
         //
         // b) for the remaining N (up to 31 or 63) bytes use the first N
         // bytes of digest DS
         /*
          * Create byte sequence S.
          */
         // Remark: The salt is limited to 16 chars, how does this make sense?
         byte[] sBytes = new byte[saltLen];
         cp = 0;
         while (cp < saltLen - blocksize) {
             System.arraycopy(tempResult, 0, sBytes, cp, blocksize);
             cp += blocksize;
         }
         System.arraycopy(tempResult, 0, sBytes, cp, saltLen - cp);
 
         // 21. repeat a loop according to the number specified in the rounds=<N>
         // specification in the salt (or the default value if none is
         // present). Each round is numbered, starting with 0 and up to N-1.
         //
         // The loop uses a digest as input. In the first round it is the
         // digest produced in step 12. In the latter steps it is the digest
         // produced in step 21.h. The following text uses the notation
         // "digest A/C" to describe this behavior.
         /*
          * Repeatedly run the collected hash value through sha512 to burn CPU cycles.
          */
         for (int i = 0; i <= rounds - 1; i++) {
             // a) start digest C
             /*
              * New context.
              */
             ctx = DigestUtils.getDigest(algorithm);
 
             // b) for odd round numbers add the byte sequense P to digest C
             // c) for even round numbers add digest A/C
             /*
              * Add key or last result.
              */
             if ((i & 1) != 0) {
                 ctx.update(pBytes, 0, keyLen);
             } else {
                 ctx.update(altResult, 0, blocksize);
             }
 
             // d) for all round numbers not divisible by 3 add the byte sequence S
             /*
              * Add salt for numbers not divisible by 3.
              */
             if (i % 3 != 0) {
                 ctx.update(sBytes, 0, saltLen);
             }
 
             // e) for all round numbers not divisible by 7 add the byte sequence P
             /*
              * Add key for numbers not divisible by 7.
              */
             if (i % 7 != 0) {
                 ctx.update(pBytes, 0, keyLen);
             }
 
             // f) for odd round numbers add digest A/C
             // g) for even round numbers add the byte sequence P
             /*
              * Add key or last result.
              */
             if ((i & 1) != 0) {
                 ctx.update(altResult, 0, blocksize);
             } else {
                 ctx.update(pBytes, 0, keyLen);
             }
 
             // h) finish digest C.
             /*
              * Create intermediate result.
              */
             altResult = ctx.digest();
         }
 
         // 22. Produce the output string. This is an ASCII string of the maximum
         // size specified above, consisting of multiple pieces:
         //
         // a) the salt salt_prefix, $5$ or $6$ respectively
         //
         // b) the rounds=<N> specification, if one was present in the input
         // salt string. A trailing '$' is added in this case to separate
         // the rounds specification from the following text.
         //
         // c) the salt string truncated to 16 characters
         //
         // d) a '$' character
         /*
          * Now we can construct the result string. It consists of three parts.
          */
         StringBuilder buffer = new StringBuilder(saltPrefix);
         if (roundsCustom) {
             buffer.append(ROUNDS_PREFIX);
             buffer.append(rounds);
             buffer.append("$");
         }
         buffer.append(saltString);
         buffer.append("$");
 
         // e) the base-64 encoded final C digest. The encoding used is as
         // follows:
         // [...]
         //
         // Each group of three bytes from the digest produces four
         // characters as output:
         //
         // 1. character: the six low bits of the first byte
         // 2. character: the two high bits of the first byte and the
         // four low bytes from the second byte
         // 3. character: the four high bytes from the second byte and
         // the two low bits from the third byte
         // 4. character: the six high bits from the third byte
         //
         // The groups of three bytes are as follows (in this sequence).
         // These are the indices into the byte array containing the
         // digest, starting with index 0. For the last group there are
         // not enough bytes left in the digest and the value zero is used
         // in its place. This group also produces only three or two
         // characters as output for SHA-512 and SHA-512 respectively.
 
         // This was just a safeguard in the C implementation:
         // int buflen = salt_prefix.length() - 1 + ROUNDS_PREFIX.length() + 9 + 1 + salt_string.length() + 1 + 86 + 1;
 
         if (blocksize == 32) {
             B64.b64from24bit(altResult[0], altResult[10], altResult[20], 4, buffer);
             B64.b64from24bit(altResult[21], altResult[1], altResult[11], 4, buffer);
             B64.b64from24bit(altResult[12], altResult[22], altResult[2], 4, buffer);
             B64.b64from24bit(altResult[3], altResult[13], altResult[23], 4, buffer);
             B64.b64from24bit(altResult[24], altResult[4], altResult[14], 4, buffer);
             B64.b64from24bit(altResult[15], altResult[25], altResult[5], 4, buffer);
             B64.b64from24bit(altResult[6], altResult[16], altResult[26], 4, buffer);
             B64.b64from24bit(altResult[27], altResult[7], altResult[17], 4, buffer);
             B64.b64from24bit(altResult[18], altResult[28], altResult[8], 4, buffer);
             B64.b64from24bit(altResult[9], altResult[19], altResult[29], 4, buffer);
             B64.b64from24bit((byte) 0, altResult[31], altResult[30], 3, buffer);
         } else {
             B64.b64from24bit(altResult[0], altResult[21], altResult[42], 4, buffer);
             B64.b64from24bit(altResult[22], altResult[43], altResult[1], 4, buffer);
             B64.b64from24bit(altResult[44], altResult[2], altResult[23], 4, buffer);
             B64.b64from24bit(altResult[3], altResult[24], altResult[45], 4, buffer);
             B64.b64from24bit(altResult[25], altResult[46], altResult[4], 4, buffer);
             B64.b64from24bit(altResult[47], altResult[5], altResult[26], 4, buffer);
             B64.b64from24bit(altResult[6], altResult[27], altResult[48], 4, buffer);
             B64.b64from24bit(altResult[28], altResult[49], altResult[7], 4, buffer);
             B64.b64from24bit(altResult[50], altResult[8], altResult[29], 4, buffer);
             B64.b64from24bit(altResult[9], altResult[30], altResult[51], 4, buffer);
             B64.b64from24bit(altResult[31], altResult[52], altResult[10], 4, buffer);
             B64.b64from24bit(altResult[53], altResult[11], altResult[32], 4, buffer);
             B64.b64from24bit(altResult[12], altResult[33], altResult[54], 4, buffer);
             B64.b64from24bit(altResult[34], altResult[55], altResult[13], 4, buffer);
             B64.b64from24bit(altResult[56], altResult[14], altResult[35], 4, buffer);
             B64.b64from24bit(altResult[15], altResult[36], altResult[57], 4, buffer);
             B64.b64from24bit(altResult[37], altResult[58], altResult[16], 4, buffer);
             B64.b64from24bit(altResult[59], altResult[17], altResult[38], 4, buffer);
             B64.b64from24bit(altResult[18], altResult[39], altResult[60], 4, buffer);
             B64.b64from24bit(altResult[40], altResult[61], altResult[19], 4, buffer);
             B64.b64from24bit(altResult[62], altResult[20], altResult[41], 4, buffer);
             B64.b64from24bit((byte) 0, (byte) 0, altResult[63], 2, buffer);
         }
 
         /*
          * Clear the buffer for the intermediate result so that people attaching to processes or reading core dumps
          * cannot get any information.
          */
         // Is there a better way to do this with the JVM?
         Arrays.fill(tempResult, (byte) 0);
         Arrays.fill(pBytes, (byte) 0);
         Arrays.fill(sBytes, (byte) 0);
         ctx.reset();
         altCtx.reset();
         Arrays.fill(keyBytes, (byte) 0);
         Arrays.fill(saltBytes, (byte) 0);
 
         return buffer.toString();
     }
 
     /**
      * Generates a libc crypt() compatible "$6$" hash value with random salt.
      * <p>
      * See {@link Crypt#crypt(String, String)} for details.
      *
      * @throws RuntimeException
      *             when a {@link java.security.NoSuchAlgorithmException} is caught.
      */
     public static String sha512Crypt(byte[] keyBytes) {
         return sha512Crypt(keyBytes, null);
     }
 
     /**
      * Generates a libc6 crypt() compatible "$6$" hash value.
      * <p>
      * See {@link Crypt#crypt(String, String)} for details.
      *
      * @throws IllegalArgumentException
      *             if the salt does not match the allowed pattern
      * @throws RuntimeException
      *             when a {@link java.security.NoSuchAlgorithmException} is caught.
      */
     public static String sha512Crypt(byte[] keyBytes, String salt) {
         if (salt == null) {
             salt = SHA512_PREFIX + B64.getRandomSalt(8);
         }
         return sha2Crypt(keyBytes, salt, SHA512_PREFIX, SHA512_BLOCKSIZE, MessageDigestAlgorithms.SHA_512);
     }
 }