//
// X509Certificates.cs: Handles X.509 certificates.
//
// Author:
//	Sebastien Pouliot  <sebastien@xamarin.com>
//
// (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
// Copyright (C) 2004-2006 Novell, Inc (http://www.novell.com)
// Copyright 2013 Xamarin Inc. (http://www.xamarin.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Runtime.Serialization;
using System.Security.Cryptography;
using SSCX = System.Security.Cryptography.X509Certificates;
using System.Security.Permissions;
using System.Text;
using Mono.Security.Cryptography;

namespace Mono.Security.X509 {

	// References:
	// a.	Internet X.509 Public Key Infrastructure Certificate and CRL Profile
	//	http://www.ietf.org/rfc/rfc3280.txt
	// b.	ITU ASN.1 standards (free download)
	//	http://www.itu.int/ITU-T/studygroups/com17/languages/

#if INSIDE_CORLIB
	internal class X509Certificate : ISerializable {
#else
	public class X509Certificate : ISerializable {
#endif

		private ASN1 decoder;

		private byte[] m_encodedcert;
		private DateTime m_from;
		private DateTime m_until;
		private ASN1 issuer;
		private string m_issuername;
		private string m_keyalgo;
		private byte[] m_keyalgoparams;
		private ASN1 subject;
		private string m_subject;
		private byte[] m_publickey;
		private byte[] signature;
		private string m_signaturealgo;
		private byte[] m_signaturealgoparams;
		private byte[] certhash;
		private RSA _rsa;
		private DSA _dsa;

		// from http://msdn.microsoft.com/en-gb/library/ff635835.aspx
		private const string OID_DSA = "1.2.840.10040.4.1";
		private const string OID_RSA = "1.2.840.113549.1.1.1";
		
		// from http://www.ietf.org/rfc/rfc2459.txt
		//
		//Certificate  ::=  SEQUENCE  {
		//     tbsCertificate       TBSCertificate,
		//     signatureAlgorithm   AlgorithmIdentifier,
		//     signature            BIT STRING  }
		//
		//TBSCertificate  ::=  SEQUENCE  {
		//     version         [0]  Version DEFAULT v1,
		//     serialNumber         CertificateSerialNumber,
		//     signature            AlgorithmIdentifier,
		//     issuer               Name,
		//     validity             Validity,
		//     subject              Name,
		//     subjectPublicKeyInfo SubjectPublicKeyInfo,
		//     issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
		//                          -- If present, version shall be v2 or v3
		//     subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
		//                          -- If present, version shall be v2 or v3
		//     extensions      [3]  Extensions OPTIONAL
		//                          -- If present, version shall be v3 --  }
		private int version;
		private byte[] serialnumber;

		private byte[] issuerUniqueID;
		private byte[] subjectUniqueID;
		private X509ExtensionCollection extensions;

		private static string encoding_error = ("Input data cannot be coded as a valid certificate.");


		// that's were the real job is!
		private void Parse (byte[] data) 
		{
			try {
				decoder = new ASN1 (data);
				// Certificate 
				if (decoder.Tag != 0x30)
					throw new CryptographicException (encoding_error);
				// Certificate / TBSCertificate
				if (decoder [0].Tag != 0x30)
					throw new CryptographicException (encoding_error);

				ASN1 tbsCertificate = decoder [0];

				int tbs = 0;
				// Certificate / TBSCertificate / Version
				ASN1 v = decoder [0][tbs];
				version = 1;			// DEFAULT v1
				if ((v.Tag == 0xA0) && (v.Count > 0)) {
					// version (optional) is present only in v2+ certs
					version += v [0].Value [0];	// zero based
					tbs++;
				}

				// Certificate / TBSCertificate / CertificateSerialNumber
				ASN1 sn = decoder [0][tbs++];
				if (sn.Tag != 0x02) 
					throw new CryptographicException (encoding_error);
				serialnumber = sn.Value;
				Array.Reverse (serialnumber, 0, serialnumber.Length);
		
				// Certificate / TBSCertificate / AlgorithmIdentifier
				tbs++;
				// ASN1 signatureAlgo = tbsCertificate.Element (tbs++, 0x30); 
		
				issuer = tbsCertificate.Element (tbs++, 0x30); 
				m_issuername = X501.ToString (issuer);
		
				ASN1 validity = tbsCertificate.Element (tbs++, 0x30);
				ASN1 notBefore = validity [0];
				m_from = ASN1Convert.ToDateTime (notBefore);
				ASN1 notAfter = validity [1];
				m_until = ASN1Convert.ToDateTime (notAfter);
		
				subject = tbsCertificate.Element (tbs++, 0x30);
				m_subject = X501.ToString (subject);
		
				ASN1 subjectPublicKeyInfo = tbsCertificate.Element (tbs++, 0x30);
		
				ASN1 algorithm = subjectPublicKeyInfo.Element (0, 0x30);
				ASN1 algo = algorithm.Element (0, 0x06);
				m_keyalgo = ASN1Convert.ToOid (algo);
				// parameters ANY DEFINED BY algorithm OPTIONAL
				// so we dont ask for a specific (Element) type and return DER
				ASN1 parameters = algorithm [1];
				m_keyalgoparams = ((algorithm.Count > 1) ? parameters.GetBytes () : null);
		
				ASN1 subjectPublicKey = subjectPublicKeyInfo.Element (1, 0x03); 
				// we must drop th first byte (which is the number of unused bits
				// in the BITSTRING)
				int n = subjectPublicKey.Length - 1;
				m_publickey = new byte [n];
				Buffer.BlockCopy (subjectPublicKey.Value, 1, m_publickey, 0, n);

				// signature processing
				byte[] bitstring = decoder [2].Value;
				// first byte contains unused bits in first byte
				signature = new byte [bitstring.Length - 1];
				Buffer.BlockCopy (bitstring, 1, signature, 0, signature.Length);

				algorithm = decoder [1];
				algo = algorithm.Element (0, 0x06);
				m_signaturealgo = ASN1Convert.ToOid (algo);
				parameters = algorithm [1];
				if (parameters != null)
					m_signaturealgoparams = parameters.GetBytes ();
				else
					m_signaturealgoparams = null;

				// Certificate / TBSCertificate / issuerUniqueID
				ASN1 issuerUID = tbsCertificate.Element (tbs, 0x81);
				if (issuerUID != null) {
					tbs++;
					issuerUniqueID = issuerUID.Value;
				}

				// Certificate / TBSCertificate / subjectUniqueID
				ASN1 subjectUID = tbsCertificate.Element (tbs, 0x82);
				if (subjectUID != null) {
					tbs++;
					subjectUniqueID = subjectUID.Value;
				}

				// Certificate / TBSCertificate / Extensions
				ASN1 extns = tbsCertificate.Element (tbs, 0xA3);
				if ((extns != null) && (extns.Count == 1))
					extensions = new X509ExtensionCollection (extns [0]);
				else
					extensions = new X509ExtensionCollection (null);

				// keep a copy of the original data
				m_encodedcert = (byte[]) data.Clone ();
			}
			catch (Exception ex) {
				throw new CryptographicException (encoding_error, ex);
			}
		}

		// constructors

		public X509Certificate (byte[] data) 
		{
			if (data != null) {
				// does it looks like PEM ?
				if ((data.Length > 0) && (data [0] != 0x30)) {
					try {
						data = PEM ("CERTIFICATE", data);
					}
					catch (Exception ex) {
						throw new CryptographicException (encoding_error, ex);
					}
				}
				Parse (data);
			}
		}

		private byte[] GetUnsignedBigInteger (byte[] integer) 
		{
			if (integer [0] == 0x00) {
				// this first byte is added so we're sure it's an unsigned integer
				// however we can't feed it into RSAParameters or DSAParameters
				int length = integer.Length - 1;
				byte[] uinteger = new byte [length];
				Buffer.BlockCopy (integer, 1, uinteger, 0, length);
				return uinteger;
			}
			else
				return integer;
		}

		// public methods

		public DSA DSA {
			get {
				if (m_keyalgoparams == null)
					throw new CryptographicException ("Missing key algorithm parameters.");

				if (_dsa == null && m_keyalgo == OID_DSA) {
					DSAParameters dsaParams = new DSAParameters ();
					// for DSA m_publickey contains 1 ASN.1 integer - Y
					ASN1 pubkey = new ASN1 (m_publickey);
					if ((pubkey == null) || (pubkey.Tag != 0x02))
						return null;
					dsaParams.Y = GetUnsignedBigInteger (pubkey.Value);

					ASN1 param = new ASN1 (m_keyalgoparams);
					if ((param == null) || (param.Tag != 0x30) || (param.Count < 3))
						return null;
					if ((param [0].Tag != 0x02) || (param [1].Tag != 0x02) || (param [2].Tag != 0x02))
						return null;
					dsaParams.P = GetUnsignedBigInteger (param [0].Value);
					dsaParams.Q = GetUnsignedBigInteger (param [1].Value);
					dsaParams.G = GetUnsignedBigInteger (param [2].Value);

					// BUG: MS BCL 1.0 can't import a key which 
					// isn't the same size as the one present in
					// the container.
					_dsa = (DSA) new DSACryptoServiceProvider (dsaParams.Y.Length << 3);
					_dsa.ImportParameters (dsaParams);
				}
				return _dsa; 
			}

			set {
				_dsa = value;
				if (value != null)
					_rsa = null;
			}
		}

		public X509ExtensionCollection Extensions {
			get { return extensions; }
		}

		public byte[] Hash {
			get {
				if (certhash == null) {
					if ((decoder == null) || (decoder.Count < 1))
						return null;
					string algo = PKCS1.HashNameFromOid (m_signaturealgo, false);
					if (algo == null)
						return null;
					byte[] toBeSigned = decoder [0].GetBytes ();
					using (var hash = PKCS1.CreateFromName (algo))
						certhash = hash.ComputeHash (toBeSigned, 0, toBeSigned.Length);
				}
				return (byte[]) certhash.Clone ();
			}
		}

		public virtual string IssuerName {
			get { return m_issuername; }
		}

		public virtual string KeyAlgorithm {
			get { return m_keyalgo; }
		}

		public virtual byte[] KeyAlgorithmParameters {
			get {
				if (m_keyalgoparams == null)
					return null;
				return (byte[]) m_keyalgoparams.Clone (); 
			}
			set { m_keyalgoparams = value; }
		}

		public virtual byte[] PublicKey	{
			get { 
				if (m_publickey == null)
					return null;
				return (byte[]) m_publickey.Clone ();
			}
		}

		public virtual RSA RSA {
			get {
				if (_rsa == null && m_keyalgo == OID_RSA) {
					RSAParameters rsaParams = new RSAParameters ();
					// for RSA m_publickey contains 2 ASN.1 integers
					// the modulus and the public exponent
					ASN1 pubkey = new ASN1 (m_publickey);
					ASN1 modulus = pubkey [0];
					if ((modulus == null) || (modulus.Tag != 0x02))
						return null;
					ASN1 exponent = pubkey [1];
					if (exponent.Tag != 0x02)
						return null;

					rsaParams.Modulus = GetUnsignedBigInteger (modulus.Value);
					rsaParams.Exponent = exponent.Value;

					// BUG: MS BCL 1.0 can't import a key which 
					// isn't the same size as the one present in
					// the container.
					int keySize = (rsaParams.Modulus.Length << 3);
					_rsa = (RSA) new RSACryptoServiceProvider (keySize);
					_rsa.ImportParameters (rsaParams);
				}
				return _rsa; 
			}

			set {
				if (value != null)
					_dsa = null;
				_rsa = value;
			}
		}
	        
		public virtual byte[] RawData {
			get {
				if (m_encodedcert == null)
					return null;
				return (byte[]) m_encodedcert.Clone ();
			}
		}

		public virtual byte[] SerialNumber {
			get { 
				if (serialnumber == null)
					return null;
				return (byte[]) serialnumber.Clone (); 
			}
		}

		public virtual byte[] Signature {
			get { 
				if (signature == null)
					return null;

				switch (m_signaturealgo) {
					case "1.2.840.113549.1.1.2":	// MD2 with RSA encryption 
					case "1.2.840.113549.1.1.3":	// MD4 with RSA encryption 
					case "1.2.840.113549.1.1.4":	// MD5 with RSA encryption 
					case "1.2.840.113549.1.1.5":	// SHA-1 with RSA Encryption 
					case "1.3.14.3.2.29":		// SHA1 with RSA signature
					case "1.2.840.113549.1.1.11":	// SHA-256 with RSA Encryption
					case "1.2.840.113549.1.1.12":	// SHA-384 with RSA Encryption
					case "1.2.840.113549.1.1.13":	// SHA-512 with RSA Encryption
					case "1.3.36.3.3.1.2":			// RIPEMD160 with RSA Encryption
						return (byte[]) signature.Clone ();

					case "1.2.840.10040.4.3":	// SHA-1 with DSA
						ASN1 sign = new ASN1 (signature);
						if ((sign == null) || (sign.Count != 2))
							return null;
						byte[] part1 = sign [0].Value;
						byte[] part2 = sign [1].Value;
						byte[] sig = new byte [40];
						// parts may be less than 20 bytes (i.e. first bytes were 0x00)
						// parts may be more than 20 bytes (i.e. first byte > 0x80, negative)
						int s1 = System.Math.Max (0, part1.Length - 20);
						int e1 = System.Math.Max (0, 20 - part1.Length);
						Buffer.BlockCopy (part1, s1, sig, e1, part1.Length - s1);
						int s2 = System.Math.Max (0, part2.Length - 20);
						int e2 = System.Math.Max (20, 40 - part2.Length);
						Buffer.BlockCopy (part2, s2, sig, e2, part2.Length - s2);
						return sig;

					default:
						throw new CryptographicException ("Unsupported hash algorithm: " + m_signaturealgo);
				}
			}
		}

		public virtual string SignatureAlgorithm {
			get { return m_signaturealgo; }
		}

		public virtual byte[] SignatureAlgorithmParameters {
			get { 
				if (m_signaturealgoparams == null)
					return m_signaturealgoparams;
				return (byte[]) m_signaturealgoparams.Clone ();
			}
		}

		public virtual string SubjectName {
			get { return m_subject; }
		}

		public virtual DateTime ValidFrom {
			get { return m_from; }
		}

		public virtual DateTime ValidUntil {
			get { return m_until; }
		}

		public int Version {
			get { return version; }
		}

		public bool IsCurrent {
			get { return WasCurrent (DateTime.UtcNow); }
		}

		public bool WasCurrent (DateTime instant) 
		{
			return ((instant > ValidFrom) && (instant <= ValidUntil));
		}

		// uncommon v2 "extension"
		public byte[] IssuerUniqueIdentifier {
			get {
				if (issuerUniqueID == null)
					return null;
				return (byte[]) issuerUniqueID.Clone ();
			}
		}

		// uncommon v2 "extension"
		public byte[] SubjectUniqueIdentifier {
			get {
				if (subjectUniqueID == null)
					return null;
				return (byte[]) subjectUniqueID.Clone ();
			}
		}

		internal bool VerifySignature (DSA dsa) 
		{
			// signatureOID is check by both this.Hash and this.Signature
			DSASignatureDeformatter v = new DSASignatureDeformatter (dsa);
			// only SHA-1 is supported
			v.SetHashAlgorithm ("SHA1");
			return v.VerifySignature (this.Hash, this.Signature);
		}

		internal bool VerifySignature (RSA rsa) 
		{
			// SHA1-1 with DSA
			if (m_signaturealgo == "1.2.840.10040.4.3")
				return false;
			RSAPKCS1SignatureDeformatter v = new RSAPKCS1SignatureDeformatter (rsa);
			v.SetHashAlgorithm (PKCS1.HashNameFromOid (m_signaturealgo));
			return v.VerifySignature (this.Hash, this.Signature);
		}

		public bool VerifySignature (AsymmetricAlgorithm aa) 
		{
			if (aa == null)
				throw new ArgumentNullException ("aa");

			if (aa is RSA)
				return VerifySignature (aa as RSA);
			else if (aa is DSA)
				return VerifySignature (aa as DSA);
			else 
				throw new NotSupportedException ("Unknown Asymmetric Algorithm " + aa.ToString ());
		}

		public bool CheckSignature (byte[] hash, string hashAlgorithm, byte[] signature) 
		{
			RSACryptoServiceProvider r = (RSACryptoServiceProvider) RSA;
			return r.VerifyHash (hash, hashAlgorithm, signature);
		}

		public bool IsSelfSigned {
			get { 
				if (m_issuername != m_subject)
					return false;

				try {
					if (RSA != null)
						return VerifySignature (RSA);
					else if (DSA != null)
						return VerifySignature (DSA);
					else
						return false; // e.g. a certificate with only DSA parameters
				}
				catch (CryptographicException) {
					return false;
				}
			}
		}

		public ASN1 GetIssuerName ()
		{
			return issuer;
		}

		public ASN1 GetSubjectName ()
		{
			return subject;
		}

		protected X509Certificate (SerializationInfo info, StreamingContext context)
		{
			Parse ((byte[]) info.GetValue ("raw", typeof (byte[])));
		}

		[SecurityPermission (SecurityAction.Demand, SerializationFormatter = true)]
		public virtual void GetObjectData (SerializationInfo info, StreamingContext context)
		{
			info.AddValue ("raw", m_encodedcert);
			// note: we NEVER serialize the private key
		}

		static byte[] PEM (string type, byte[] data) 
		{
			string pem = Encoding.ASCII.GetString (data);
			string header = String.Format ("-----BEGIN {0}-----", type);
			string footer = String.Format ("-----END {0}-----", type);
			int start = pem.IndexOf (header) + header.Length;
			int end = pem.IndexOf (footer, start);
			string base64 = pem.Substring (start, (end - start));
			return Convert.FromBase64String (base64);
		}
	}
}