public static boolean verifySignature()

in cvs/trilead-ssh2-build213/src/com/trilead/ssh2/signature/RSASHA1Verify.java [144:284]
107 lines of code
21 McCabe index (conditional complexity)

	public static boolean verifySignature(byte[] message, RSASignature ds, RSAPublicKey dpk) throws IOException
	{
		SHA1 md = new SHA1();
		md.update(message);
		byte[] sha_message = new byte[md.getDigestLength()];
		md.digest(sha_message);

		BigInteger n = dpk.getN();
		BigInteger e = dpk.getE();
		BigInteger s = ds.getS();

		if (n.compareTo(s) <= 0)
		{
			log.log(20, "ssh-rsa signature: n.compareTo(s) <= 0");
			return false;
		}

		int rsa_block_len = (n.bitLength() + 7) / 8;

		/* And now the show begins */

		if (rsa_block_len < 1)
		{
			log.log(20, "ssh-rsa signature: rsa_block_len < 1");
			return false;
		}

		byte[] v = s.modPow(e, n).toByteArray();

		int startpos = 0;

		if ((v.length > 0) && (v[0] == 0x00))
			startpos++;

		if ((v.length - startpos) != (rsa_block_len - 1))
		{
			log.log(20, "ssh-rsa signature: (v.length - startpos) != (rsa_block_len - 1)");
			return false;
		}

		if (v[startpos] != 0x01)
		{
			log.log(20, "ssh-rsa signature: v[startpos] != 0x01");
			return false;
		}

		int pos = startpos + 1;

		while (true)
		{
			if (pos >= v.length)
			{
				log.log(20, "ssh-rsa signature: pos >= v.length");
				return false;
			}
			if (v[pos] == 0x00)
				break;
			if (v[pos] != (byte) 0xff)
			{
				log.log(20, "ssh-rsa signature: v[pos] != (byte) 0xff");
				return false;
			}
			pos++;
		}

		int num_pad = pos - (startpos + 1);

		if (num_pad < 8)
		{
			log.log(20, "ssh-rsa signature: num_pad < 8");
			return false;
		}

		pos++;

		if (pos >= v.length)
		{
			log.log(20, "ssh-rsa signature: pos >= v.length");
			return false;
		}

		SimpleDERReader dr = new SimpleDERReader(v, pos, v.length - pos);

		byte[] seq = dr.readSequenceAsByteArray();

		if (dr.available() != 0)
		{
			log.log(20, "ssh-rsa signature: dr.available() != 0");
			return false;
		}

		dr.resetInput(seq);

		/* Read digestAlgorithm */

		byte digestAlgorithm[] = dr.readSequenceAsByteArray();

		/* Inspired by RFC 3347, however, ignoring the comment regarding old BER based implementations */

		if ((digestAlgorithm.length < 8) || (digestAlgorithm.length > 9))
		{
			log.log(20, "ssh-rsa signature: (digestAlgorithm.length < 8) || (digestAlgorithm.length > 9)");
			return false;
		}

		byte[] digestAlgorithm_sha1 = new byte[] { 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00 };

		for (int i = 0; i < digestAlgorithm.length; i++)
		{
			if (digestAlgorithm[i] != digestAlgorithm_sha1[i])
			{
				log.log(20, "ssh-rsa signature: digestAlgorithm[i] != digestAlgorithm_sha1[i]");
				return false;
			}
		}

		byte[] digest = dr.readOctetString();

		if (dr.available() != 0)
		{
			log.log(20, "ssh-rsa signature: dr.available() != 0 (II)");
			return false;
		}
			
		if (digest.length != sha_message.length)
		{
			log.log(20, "ssh-rsa signature: digest.length != sha_message.length");
			return false;
		}

		for (int i = 0; i < sha_message.length; i++)
		{
			if (sha_message[i] != digest[i])
			{
				log.log(20, "ssh-rsa signature: sha_message[i] != digest[i]");
				return false;
			}
		}

		return true;
	}