Java by API/java.security/Security

Security: addProvider(Provider provider)

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.Provider;
import java.security.Security;
import java.util.zip.CRC32;
public class MainClass {
  static private String hexDigit(byte x) {
    StringBuffer sb = new StringBuffer();
    char c;
    // First nibble
    c = (char) ((x >> 4) & 0xf);
    if (c > 9) {
      c = (char) ((c - 10) + "a");
    } else {
      c = (char) (c + "0");
    }
    sb.append(c);
    // Second nibble
    c = (char) (x & 0xf);
    if (c > 9) {
      c = (char) ((c - 10) + "a");
    } else {
      c = (char) (c + "0");
    }
    sb.append(c);
    return sb.toString();
  }
  static private String computeDigest(MessageDigest algorithm, String filename) {
    String returnValue = "";
    try {
      algorithm.reset();
      FileInputStream fis = new FileInputStream(filename);
      BufferedInputStream bis = new BufferedInputStream(fis);
      DigestInputStream dis = new DigestInputStream(bis, algorithm);
      int ch;
      while ((ch = dis.read()) != -1)
        ;
      StringBuffer hexString = new StringBuffer();
      byte digest[] = algorithm.digest();
      int digestLength = digest.length;
      for (int i = 0; i < digestLength; i++) {
        hexString.append(hexDigit(digest[i]));
        hexString.append(" ");
      }
      returnValue = hexString.toString();
    } catch (IOException e) {
      System.err.println("Error generating digest for: " + filename);
    }
    return returnValue;
  }
  public static void main(String args[]) {
    MessageDigest algorithm = null;
    Security.addProvider(new MyProvider());
    try {
      algorithm = MessageDigest.getInstance("CRC32");
    } catch (NoSuchAlgorithmException e) {
      System.err.println("Invalid algorithm");
      System.exit(-1);
    }
    int argsLength = args.length;
    for (int i = 0; i < argsLength; i++) {
      String digest = computeDigest(algorithm, args[i]);
      System.out.println(args[i] + " : " + digest);
    }
  }
}
class MyProvider extends Provider {
  public MyProvider() {
    super("MyProvider", 1.0, "jexp.ru Collections Example");
    put("CRC32", "CRC");
  }
}
class CRC extends MessageDigest {
  CRC32 crc;
  public CRC() {
    super("CRC");
    crc = new CRC32();
  }
  protected void engineReset() {
    crc.reset();
  }
  protected void engineUpdate(byte input) {
    crc.update(input);
  }
  protected void engineUpdate(byte[] input, int offset, int len) {
    crc.update(input, offset, len);
  }
  protected byte[] engineDigest() {
    long l = crc.getValue();
    byte[] bytes = new byte[4];
    bytes[3] = (byte) ((l & 0xFF000000) >> 24);
    bytes[2] = (byte) ((l & 0x00FF0000) >> 16);
    bytes[1] = (byte) ((l & 0x0000FF00) >> 8);
    bytes[0] = (byte) ((l & 0x000000FF) >> 0);
    return bytes;
  }
}

Security: getProviders()

/*
Ciphers:
            None available.
KeyAgreeents:
            None available.
Macs:
            None available.
MessageDigests:
            SHA-512
            SHA1
            MD2
            SHA
            SHA ImplementedIn
            SHA-256
            MD5 ImplementedIn
            SHA-1
            MD5
            SHA-384
Signatures:
            OID.1.2.840.10040.4.3
            OID.1.2.840.113549.1.1.4
            SHA384withRSA
            1.3.14.3.2.29
            SHA512withRSA SupportedKeyClasses
            SHA/DSA
            SHA1withDSA KeySize
            NONEwithDSA SupportedKeyClasses
            OID.1.2.840.113549.1.1.5
            SHA512withRSA
            MD5withRSA
            DSS
            OID.1.2.840.113549.1.1.11
            SHA384withRSA SupportedKeyClasses
            SHA1withRSA
            MD5withRSA SupportedKeyClasses
            NONEwithDSA
            1.2.840.113549.1.1.4
            MD5andSHA1withRSA
            1.2.840.113549.1.1.11
            OID.1.2.840.113549.1.1.13
            1.3.14.3.2.27
            1.2.840.10040.4.3
            SHA256withRSA
            MD2withRSA SupportedKeyClasses
            1.2.840.113549.1.1.2
            1.2.840.113549.1.1.12
            RawDSA
            SHA1withDSA
            SHA1/DSA
            MD2withRSA
            1.3.14.3.2.13
            SHAwithDSA
            DSAWithSHA1
            1.2.840.113549.1.1.13
            OID.1.3.14.3.2.29
            SHA1withDSA ImplementedIn
            SHA256withRSA SupportedKeyClasses
            SHA1withDSA SupportedKeyClasses
            DSA
            1.2.840.113549.1.1.5
            SHA-1/DSA
            SHA1withRSA SupportedKeyClasses
            OID.1.2.840.113549.1.1.12
            OID.1.2.840.113549.1.1.2
 */
import java.security.Provider;
import java.security.Security;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
public class ListAlgorithms {
  public static void printSet(String setName, Set algorithms) {
    System.out.println(setName + ":");
    if (algorithms.isEmpty()) {
      System.out.println("            None available.");
    } else {
      Iterator it = algorithms.iterator();
      while (it.hasNext()) {
        String name = (String) it.next();
        System.out.println("            " + name);
      }
    }
  }
  public static void main(String[] args) {
    Provider[] providers = Security.getProviders();
    Set<String> ciphers = new HashSet<String>();
    Set<String> keyAgreements = new HashSet<String>();
    Set<String> macs = new HashSet<String>();
    Set<String> messageDigests = new HashSet<String>();
    Set<String> signatures = new HashSet<String>();
    for (int i = 0; i != providers.length; i++) {
      Iterator it = providers[i].keySet().iterator();
      while (it.hasNext()) {
        String entry = (String) it.next();
        if (entry.startsWith("Alg.Alias.")) {
          entry = entry.substring("Alg.Alias.".length());
        }
        if (entry.startsWith("Cipher.")) {
          ciphers.add(entry.substring("Cipher.".length()));
        } else if (entry.startsWith("KeyAgreement.")) {
          keyAgreements.add(entry.substring("KeyAgreement.".length()));
        } else if (entry.startsWith("Mac.")) {
          macs.add(entry.substring("Mac.".length()));
        } else if (entry.startsWith("MessageDigest.")) {
          messageDigests.add(entry.substring("MessageDigest.".length()));
        } else if (entry.startsWith("Signature.")) {
          signatures.add(entry.substring("Signature.".length()));
        }
      }
    }
    printSet("Ciphers", ciphers);
    printSet("KeyAgreeents", keyAgreements);
    printSet("Macs", macs);
    printSet("MessageDigests", messageDigests);
    printSet("Signatures", signatures);
  }
}