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The core random number generators
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package prng.generator;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.Provider;

/**
 * Specification for a Hash based RNG
 */
public class HashSpec {

  /**
   * Specification for SHA-1 based generator. The 440 bit seed length is the maximum number of bytes the SHA-1 algorithm can accept as a single block. The 440
   * bit input is padded with an 0x80 byte and a 64-bit message length value to create a 512-bit block.
   */
  public static final HashSpec SPEC_SHA1 = new HashSpec("SHA-1", 440, 160,
      128);

  /**
   * Specification for SHA-256 based generator. The 440 bit seed length is the maximum number of bytes the SHA-256 algorithm can accept as a single block. The
   * 440 bit input is padded with an 0x80 byte and a 64-bit message length value to create a 512-bit block.
   */
  public static final HashSpec SPEC_SHA256 = new HashSpec("SHA-256", 440, 256,
      256);

  /**
   * Specification for SHA-512 based generator. The 888 bit seed length is the maximum number of bytes the SHA-512 algorithm can accept as a single block. The
   * 888 bit input is padded with an 0x80 byte and a 128-bit message length value to create a 1024-bit block.
   */
  public static final HashSpec SPEC_SHA512 = new HashSpec("SHA-512", 888, 512,
      256);

  /** Name of the digest algorithm */
  public final String algorithm;

  /** Number of bytes in the digest output */
  public final int outputLength;

  /** Security provider, if needed */
  public final Provider provider;

  /** Number of seed bytes required by the algorithm */
  public final int seedLength;

  /** Effective security strength in bits */
  public final int strength;


  /**
   * Create new algorithm specification
   *
   * @param provider Provider implementation, if needed
   * @param algorithm algorithm name
   * @param bitSeedLength seed length in bits
   * @param bitOutputLength output length in bits
   * @param strength security strength in bits
   */
  public HashSpec(Provider provider, String algorithm, int bitSeedLength,
      int bitOutputLength, int strength) {
    this.provider = provider;
    this.algorithm = algorithm;
    seedLength = bitSeedLength / 8;
    outputLength = bitOutputLength / 8;
    this.strength = strength;
  }


  /**
   * Create new algorithm specification
   *
   * @param algorithm algorithm name
   * @param bitSeedLength seed length in bits
   * @param bitOutputLength output length in bits
   * @param strength security strength in bits
   */
  public HashSpec(String algorithm, int bitSeedLength, int bitOutputLength,
      int strength) {
    this(null, algorithm, bitSeedLength, bitOutputLength, strength);
  }


  /**
   * Get an instance of this Hash function
   *
   * @return a Hash instance
   */
  public MessageDigest getInstance() {
    try {
      if (provider == null) {
        return MessageDigest.getInstance(algorithm);
      }
      return MessageDigest.getInstance(algorithm, provider);
    } catch (NoSuchAlgorithmException e) {
      throw new InternalError("Algorithm " + algorithm + " not available");
    }
  }
}