Package ch.ethz.ssh2.crypto

Source Code of ch.ethz.ssh2.crypto.PEMDecoder

package ch.ethz.ssh2.crypto;

import java.io.BufferedReader;
import java.io.CharArrayReader;
import java.io.IOException;
import java.math.BigInteger;

import ch.ethz.ssh2.crypto.cipher.AES;
import ch.ethz.ssh2.crypto.cipher.BlockCipher;
import ch.ethz.ssh2.crypto.cipher.CBCMode;
import ch.ethz.ssh2.crypto.cipher.DES;
import ch.ethz.ssh2.crypto.cipher.DESede;
import ch.ethz.ssh2.crypto.digest.MD5;
import ch.ethz.ssh2.signature.DSAPrivateKey;
import ch.ethz.ssh2.signature.RSAPrivateKey;

/**
* PEM Support.
*
* @author Christian Plattner, plattner@inf.ethz.ch
* @version $Id: PEMDecoder.java,v 1.7 2006/02/02 09:11:03 cplattne Exp $
*/
public class PEMDecoder
{
  private static final int PEM_RSA_PRIVATE_KEY = 1;
  private static final int PEM_DSA_PRIVATE_KEY = 2;

  private static final int hexToInt(char c)
  {
    if ((c >= 'a') && (c <= 'f'))
    {
      return (c - 'a') + 10;
    }

    if ((c >= 'A') && (c <= 'F'))
    {
      return (c - 'A') + 10;
    }

    if ((c >= '0') && (c <= '9'))
    {
      return (c - '0');
    }

    throw new IllegalArgumentException("Need hex char");
  }

  private static byte[] hexToByteArray(String hex)
  {
    if (hex == null)
      throw new IllegalArgumentException("null argument");

    if ((hex.length() % 2) != 0)
      throw new IllegalArgumentException("Uneven string length in hex encoding.");

    byte decoded[] = new byte[hex.length() / 2];

    for (int i = 0; i < decoded.length; i++)
    {
      int hi = hexToInt(hex.charAt(i * 2));
      int lo = hexToInt(hex.charAt((i * 2) + 1));

      decoded[i] = (byte) (hi * 16 + lo);
    }

    return decoded;
  }

  private static byte[] generateKeyFromPasswordSaltWithMD5(byte[] password, byte[] salt, int keyLen)
      throws IOException
  {
    if (salt.length < 8)
      throw new IllegalArgumentException("Salt needs to be at least 8 bytes for key generation.");

    MD5 md5 = new MD5();

    byte[] key = new byte[keyLen];
    byte[] tmp = new byte[md5.getDigestLength()];

    while (true)
    {
      md5.update(password, 0, password.length);
      md5.update(salt, 0, 8); // ARGH we only use the first 8 bytes of the salt in this step.
      // This took me two hours until I got AES-xxx running.

      int copy = (keyLen < tmp.length) ? keyLen : tmp.length;

      md5.digest(tmp, 0);

      System.arraycopy(tmp, 0, key, key.length - keyLen, copy);

      keyLen -= copy;

      if (keyLen == 0)
        return key;

      md5.update(tmp, 0, tmp.length);
    }
  }

  private static byte[] removePadding(byte[] buff, int blockSize) throws IOException
  {
    /* Removes RFC 1423/PKCS #7 padding */

    int rfc_1423_padding = buff[buff.length - 1] & 0xff;

    if ((rfc_1423_padding < 1) || (rfc_1423_padding > blockSize))
      throw new IOException("Decrypted PEM has wrong padding, did you specify the correct password?");

    for (int i = 2; i <= rfc_1423_padding; i++)
    {
      if (buff[buff.length - i] != rfc_1423_padding)
        throw new IOException("Decrypted PEM has wrong padding, did you specify the correct password?");
    }

    byte[] tmp = new byte[buff.length - rfc_1423_padding];
    System.arraycopy(buff, 0, tmp, 0, buff.length - rfc_1423_padding);
    return tmp;
  }

  private static final PEMStructure parsePEM(char[] pem) throws IOException
  {
    PEMStructure ps = new PEMStructure();

    String line = null;

    BufferedReader br = new BufferedReader(new CharArrayReader(pem));

    String endLine = null;

    while (true)
    {
      line = br.readLine();

      if (line == null)
        throw new IOException("Invalid PEM structure, '-----BEGIN...' missing");

      line = line.trim();

      if (line.startsWith("-----BEGIN DSA PRIVATE KEY-----"))
      {
        endLine = "-----END DSA PRIVATE KEY-----";
        ps.pemType = PEM_DSA_PRIVATE_KEY;
        break;
      }

      if (line.startsWith("-----BEGIN RSA PRIVATE KEY-----"))
      {
        endLine = "-----END RSA PRIVATE KEY-----";
        ps.pemType = PEM_RSA_PRIVATE_KEY;
        break;
      }
    }

    while (true)
    {
      line = br.readLine();

      if (line == null)
        throw new IOException("Invalid PEM structure, " + endLine + " missing");

      line = line.trim();

      int sem_idx = line.indexOf(':');

      if (sem_idx == -1)
        break;

      String name = line.substring(0, sem_idx + 1);
      String value = line.substring(sem_idx + 1);

      String values[] = value.split(",");

      for (int i = 0; i < values.length; i++)
        values[i] = values[i].trim();

      // Proc-Type: 4,ENCRYPTED
      // DEK-Info: DES-EDE3-CBC,579B6BE3E5C60483

      if ("Proc-Type:".equals(name))
      {
        ps.procType = values;
        continue;
      }

      if ("DEK-Info:".equals(name))
      {
        ps.dekInfo = values;
        continue;
      }
      /* Ignore line */
    }

    StringBuffer keyData = new StringBuffer();

    while (true)
    {
      if (line == null)
        throw new IOException("Invalid PEM structure, " + endLine + " missing");

      line = line.trim();

      if (line.startsWith(endLine))
        break;

      keyData.append(line);

      line = br.readLine();
    }

    char[] pem_chars = new char[keyData.length()];
    keyData.getChars(0, pem_chars.length, pem_chars, 0);

    ps.data = Base64.decode(pem_chars);

    if (ps.data.length == 0)
      throw new IOException("Invalid PEM structure, no data available");

    return ps;
  }

  private static final void decryptPEM(PEMStructure ps, byte[] pw) throws IOException
  {
    if (ps.dekInfo == null)
      throw new IOException("Broken PEM, no mode and salt given, but encryption enabled");

    if (ps.dekInfo.length != 2)
      throw new IOException("Broken PEM, DEK-Info is incomplete!");

    String algo = ps.dekInfo[0];
    byte[] salt = hexToByteArray(ps.dekInfo[1]);

    BlockCipher bc = null;

    if (algo.equals("DES-EDE3-CBC"))
    {
      DESede des3 = new DESede();
      des3.init(false, generateKeyFromPasswordSaltWithMD5(pw, salt, 24));
      bc = new CBCMode(des3, salt, false);
    }
    else if (algo.equals("DES-CBC"))
    {
      DES des = new DES();
      des.init(false, generateKeyFromPasswordSaltWithMD5(pw, salt, 8));
      bc = new CBCMode(des, salt, false);
    }
    else if (algo.equals("AES-128-CBC"))
    {
      AES aes = new AES();
      aes.init(false, generateKeyFromPasswordSaltWithMD5(pw, salt, 16));
      bc = new CBCMode(aes, salt, false);
    }
    else if (algo.equals("AES-192-CBC"))
    {
      AES aes = new AES();
      aes.init(false, generateKeyFromPasswordSaltWithMD5(pw, salt, 24));
      bc = new CBCMode(aes, salt, false);
    }
    else if (algo.equals("AES-256-CBC"))
    {
      AES aes = new AES();
      aes.init(false, generateKeyFromPasswordSaltWithMD5(pw, salt, 32));
      bc = new CBCMode(aes, salt, false);
    }
    else
    {
      throw new IOException("Cannot decrypt PEM structure, unknown cipher " + algo);
    }

    if ((ps.data.length % bc.getBlockSize()) != 0)
      throw new IOException("Invalid PEM structure, size of encrypted block is not a multiple of "
          + bc.getBlockSize());

    /* Now decrypt the content */

    byte[] dz = new byte[ps.data.length];

    for (int i = 0; i < ps.data.length / bc.getBlockSize(); i++)
    {
      bc.transformBlock(ps.data, i * bc.getBlockSize(), dz, i * bc.getBlockSize());
    }

    /* Now check and remove RFC 1423/PKCS #7 padding */

    dz = removePadding(dz, bc.getBlockSize());

    ps.data = dz;
    ps.dekInfo = null;
    ps.procType = null;
  }

  public static final boolean isPEMEncrypted(PEMStructure ps) throws IOException
  {
    if (ps.procType == null)
      return false;

    if (ps.procType.length != 2)
      throw new IOException("Unknown Proc-Type field.");

    if ("4".equals(ps.procType[0]) == false)
      throw new IOException("Unknown Proc-Type field (" + ps.procType[0] + ")");

    if ("ENCRYPTED".equals(ps.procType[1]))
      return true;

    return false;
  }

  public static Object decode(char[] pem, String password) throws IOException
  {
    PEMStructure ps = parsePEM(pem);

    if (isPEMEncrypted(ps))
    {
      if (password == null)
        throw new IOException("PEM is encrypted, but no password was specified");

      decryptPEM(ps, password.getBytes());
    }

    if (ps.pemType == PEM_DSA_PRIVATE_KEY)
    {
      SimpleDERReader dr = new SimpleDERReader(ps.data);

      byte[] seq = dr.readSequenceAsByteArray();

      if (dr.available() != 0)
        throw new IOException("Padding in DSA PRIVATE KEY DER stream.");

      dr.resetInput(seq);

      BigInteger version = dr.readInt();

      if (version.compareTo(BigInteger.ZERO) != 0)
        throw new IOException("Wrong version (" + version + ") in DSA PRIVATE KEY DER stream.");

      BigInteger p = dr.readInt();
      BigInteger q = dr.readInt();
      BigInteger g = dr.readInt();
      BigInteger y = dr.readInt();
      BigInteger x = dr.readInt();

      if (dr.available() != 0)
        throw new IOException("Padding in DSA PRIVATE KEY DER stream.");

      return new DSAPrivateKey(p, q, g, y, x);
    }

    if (ps.pemType == PEM_RSA_PRIVATE_KEY)
    {
      SimpleDERReader dr = new SimpleDERReader(ps.data);

      byte[] seq = dr.readSequenceAsByteArray();

      if (dr.available() != 0)
        throw new IOException("Padding in RSA PRIVATE KEY DER stream.");

      dr.resetInput(seq);

      BigInteger version = dr.readInt();

      if ((version.compareTo(BigInteger.ZERO) != 0) && (version.compareTo(BigInteger.ONE) != 0))
        throw new IOException("Wrong version (" + version + ") in RSA PRIVATE KEY DER stream.");

      BigInteger n = dr.readInt();
      BigInteger e = dr.readInt();
      BigInteger d = dr.readInt();

      return new RSAPrivateKey(d, e, n);
    }

    throw new IOException("PEM problem: it is of unknown type");
  }

}
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