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finish initial support for rc4 encryption with blank user password

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Eliot Jones
2019-05-06 15:41:29 +01:00
parent 27928cd3a3
commit bad57763a1
15 changed files with 166 additions and 125 deletions
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181
src/UglyToad.PdfPig/Encryption/EncryptionHandler.cs
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@@ -2,6 +2,7 @@
{
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using CrossReference;
@@ -11,7 +12,7 @@
internal class EncryptionHandler : IEncryptionHandler
{
private static readonly byte[] PaddingBytes =
private static readonly byte[] PaddingBytes =
{
0x28, 0xBF, 0x4E, 0x5E,
0x4E, 0x75, 0x8A, 0x41,
@@ -23,6 +24,8 @@
0x64, 0x53, 0x69, 0x7A
};
private readonly HashSet<IndirectReference> previouslyDecrypted = new HashSet<IndirectReference>();
[CanBeNull]
private readonly EncryptionDictionary encryptionDictionary;
@@ -40,7 +43,7 @@
{
this.encryptionDictionary = encryptionDictionary;
documentIdBytes = trailerDictionary.Identifier != null && trailerDictionary.Identifier.Count == 2 ?
documentIdBytes = trailerDictionary.Identifier != null && trailerDictionary.Identifier.Count == 2 ?
OtherEncodings.StringAsLatin1Bytes(trailerDictionary.Identifier[0])
: EmptyArray<byte>.Instance;
this.password = password ?? string.Empty;
@@ -63,47 +66,114 @@
var passwordBytes = charset.GetBytes(this.password);
var length = encryptionDictionary.EncryptionAlgorithmCode == EncryptionAlgorithmCode.Rc4OrAes40BitKey
? 5
var length = encryptionDictionary.EncryptionAlgorithmCode == EncryptionAlgorithmCode.Rc4OrAes40BitKey
? 5
: encryptionDictionary.KeyLength.GetValueOrDefault() / 8;
encryptionKey = CalculateKeyRevisions2To4(passwordBytes, ownerKey, (int) encryptionDictionary.UserAccessPermissions, encryptionDictionary.StandardSecurityHandlerRevision,
encryptionKey = CalculateKeyRevisions2To4(passwordBytes, ownerKey, (int)encryptionDictionary.UserAccessPermissions, encryptionDictionary.StandardSecurityHandlerRevision,
length, documentIdBytes, encryptionDictionary.EncryptMetadata);
}
public IReadOnlyList<byte> Decrypt(StreamToken stream)
{
if (encryptionDictionary == null)
{
return stream?.Data;
}
if (stream == null)
{
throw new ArgumentNullException(nameof(stream));
}
throw new NotImplementedException($"Encryption is not supported yet. Encryption used in document was: {encryptionDictionary.Dictionary}.");
useAes = false;
}
public void Decrypt(IndirectReference reference, IToken token)
public IToken Decrypt(IndirectReference reference, IToken token)
{
if (token is StreamToken stream)
if (token == null)
{
throw new ArgumentNullException(nameof(token));
}
else if (token is StringToken stringToken)
{
}
else if (token is DictionaryToken dictionary)
{
}
else if (token is ArrayToken array)
{
token = DecryptInternal(reference, token);
previouslyDecrypted.Add(reference);
return token;
}
private IToken DecryptInternal(IndirectReference reference, IToken token)
{
switch (token)
{
case StreamToken stream:
{
if (stream.StreamDictionary.TryGet(NameToken.Type, out NameToken typeName))
{
if (NameToken.Xref.Equals(typeName))
{
return token;
}
if (!encryptionDictionary.EncryptMetadata && NameToken.Metadata.Equals(typeName))
{
return token;
}
// TODO: check unencrypted metadata
}
var streamDictionary = (DictionaryToken)DecryptInternal(reference, stream.StreamDictionary);
var decrypted = DecryptData(stream.Data.ToArray(), reference);
token = new StreamToken(streamDictionary, decrypted);
break;
}
case StringToken stringToken:
{
var data = OtherEncodings.StringAsLatin1Bytes(stringToken.Data);
var decrypted = DecryptData(data, reference);
token = new StringToken(OtherEncodings.BytesAsLatin1String(decrypted));
break;
}
case DictionaryToken dictionary:
{
// PDFBOX-2936: avoid orphan /CF dictionaries found in US govt "I-" files
if (dictionary.TryGet(NameToken.Cf, out _))
{
return token;
}
var isSignatureDictionary = dictionary.TryGet(NameToken.Type, out NameToken typeName)
&& (typeName.Equals(NameToken.Sig) || typeName.Equals(NameToken.DocTimeStamp));
foreach (var keyValuePair in dictionary.Data)
{
if (isSignatureDictionary && keyValuePair.Key == NameToken.Contents.Data)
{
continue;
}
if (keyValuePair.Value is StringToken || keyValuePair.Value is ArrayToken || keyValuePair.Value is DictionaryToken)
{
var inner = DecryptInternal(reference, keyValuePair.Value);
dictionary = dictionary.With(keyValuePair.Key, inner);
}
}
token = dictionary;
break;
}
case ArrayToken array:
{
var result = new IToken[array.Length];
for (var i = 0; i < array.Length; i++)
{
result[i] = DecryptInternal(reference, array.Data[i]);
}
token = new ArrayToken(result);
break;
}
}
return token;
}
private byte[] DecryptData(byte[] data, IndirectReference reference)
@@ -119,12 +189,12 @@
{
throw new NotImplementedException("Decryption for AES-128 not currently supported.");
}
return RC4.Encrypt(finalKey, data);
}
private byte[] GetObjectKey(IndirectReference reference)
{
{
// 1. Get the object and generation number from the object
// 2. Treating the object and generation number as binary integers extend the
@@ -134,13 +204,13 @@
var finalKey = new byte[encryptionKey.Length + 5 + (useAes ? 4 : 0)];
Array.Copy(encryptionKey, finalKey, encryptionKey.Length);
finalKey[encryptionKey.Length] = (byte) reference.ObjectNumber;
finalKey[encryptionKey.Length + 1] = (byte) (reference.ObjectNumber >> 1);
finalKey[encryptionKey.Length + 2] = (byte) (reference.ObjectNumber >> 2);
finalKey[encryptionKey.Length] = (byte)reference.ObjectNumber;
finalKey[encryptionKey.Length + 1] = (byte)(reference.ObjectNumber >> 8);
finalKey[encryptionKey.Length + 2] = (byte)(reference.ObjectNumber >> 16);
finalKey[encryptionKey.Length + 3] = (byte)reference.Generation;
finalKey[encryptionKey.Length + 4] = (byte)(reference.Generation >> 8);
finalKey[encryptionKey.Length + 3] = (byte) reference.Generation;
finalKey[encryptionKey.Length + 4] = (byte) (reference.Generation >> 1);
// 2. If using the AES algorithm extend the encryption key by 4 bytes by adding the value "sAlT".
if (useAes)
{
@@ -195,32 +265,28 @@
using (var md5 = MD5.Create())
{
// 2. Initialize the MD5 hash function and pass the result of step 1 as input to this function.
var has = md5.ComputeHash(passwordFull);
UpdateMd5(md5, passwordFull);
// 3. Pass the value of the encryption dictionary's owner key entry to the MD5 hash function.
var has1 = md5.ComputeHash(ownerKey);
UpdateMd5(md5, ownerKey);
// 4. Treat the value of the P entry as an unsigned 4-byte integer.
var unsigned = (uint) permissions;
var permissionsBytes = new []
{
(byte) (unsigned),
(byte) (unsigned >> 8),
(byte) (unsigned >> 16),
(byte) (unsigned >> 24)
};
var unsigned = (uint)permissions;
// 4. Pass these bytes to the MD5 hash function, low-order byte first.
var has2 = md5.ComputeHash(permissionsBytes);
UpdateMd5(md5, new[] { (byte)(unsigned) });
UpdateMd5(md5, new[] { (byte)(unsigned >> 8) });
UpdateMd5(md5, new[] { (byte)(unsigned >> 16) });
UpdateMd5(md5, new[] { (byte)(unsigned >> 24) });
// 5. Pass the first element of the file's file identifier array to the hash.
var has3 = md5.ComputeHash(documentId);
UpdateMd5(md5, documentId);
// 6. (Revision 4 or greater) If document metadata is not being encrypted, pass 4 bytes
// with the value 0xFFFFFFFF to the MD5 hash function.
if (revision >= 4)
{
md5.ComputeHash(new byte[] {0xFF, 0xFF, 0xFF, 0xFF});
UpdateMd5(md5, new byte[] { 0xFF, 0xFF, 0xFF, 0xFF });
}
// 7. Do the following 50 times: Take the output from the previous MD5 hash and
@@ -235,11 +301,13 @@
for (var i = 0; i < 50; i++)
{
md5.ComputeHash(input, 0, n);
UpdateMd5(md5, input.Take(n).ToArray());
input = md5.Hash;
}
}
md5.TransformFinalBlock(EmptyArray<byte>.Instance, 0, 0);
var result = new byte[length];
Array.Copy(md5.Hash, result, length);
@@ -248,6 +316,11 @@
}
}
private static void UpdateMd5(MD5 md5, byte[] data)
{
md5.TransformBlock(data, 0, data.Length, null, 0);
}
private static byte[] GetPaddedPassword(byte[] password)
{
if (password == null || password.Length == 0)