/*

  * 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 <drepper@redhat.com>

  * http://www.akkadia.org/drepper/SHA-crypt.txt

  * <p>

  * Conversion to Kotlin and from there to Java in 2012 by Christian Hammers <ch@lathspell.de> and likewise put

  * into the Public Domain.

  * <p>

  * This class is immutable and thread-safe.

  *

  * @version $Id$

  * @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(final 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(final 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(final byte[] keyBytes, final String salt, final String saltPrefix,

                                     final int blocksize, final String algorithm) {

         final 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");

         }

         final 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;

         }

         final String saltString = m.group(4);

         final byte[] saltBytes = saltString.getBytes(Charsets.UTF_8);

         final 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.

          */

         final 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?

         final 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.

          */

         final 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(final 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(final byte[] keyBytes, String salt) {

         if (salt == null) {

             salt = SHA512_PREFIX + B64.getRandomSalt(8);

         }

         return sha2Crypt(keyBytes, salt, SHA512_PREFIX, SHA512_BLOCKSIZE, MessageDigestAlgorithms.SHA_512);

     }

 }