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finish revision 5 and 6 owner password handling #34

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moves owner password check first. correctly calculates encryption key for owner password for revision 5 and 6.
This commit is contained in:
Eliot Jones
2019-06-25 19:44:26 +01:00
parent 76f8222f74
commit 52d2a90dfc
1 changed files with 44 additions and 24 deletions
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68
src/UglyToad.PdfPig/Encryption/EncryptionHandler.cs
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@@ -86,12 +86,7 @@
: encryptionDictionary.KeyLength.GetValueOrDefault() / 8; : encryptionDictionary.KeyLength.GetValueOrDefault() / 8;
var isUserPassword = false; var isUserPassword = false;
if (IsUserPassword(passwordBytes, encryptionDictionary, length, documentIdBytes)) if (IsOwnerPassword(passwordBytes, encryptionDictionary, length, documentIdBytes, out var userPassBytes))
{
decryptionPasswordBytes = passwordBytes;
isUserPassword = true;
}
else if (IsOwnerPassword(passwordBytes, encryptionDictionary, length, documentIdBytes, out var userPassBytes))
{ {
if (encryptionDictionary.Revision == 5 || encryptionDictionary.Revision == 6) if (encryptionDictionary.Revision == 5 || encryptionDictionary.Revision == 6)
{ {
@@ -102,6 +97,11 @@
decryptionPasswordBytes = userPassBytes; decryptionPasswordBytes = userPassBytes;
} }
} }
else if (IsUserPassword(passwordBytes, encryptionDictionary, length, documentIdBytes))
{
decryptionPasswordBytes = passwordBytes;
isUserPassword = true;
}
else else
{ {
throw new PdfDocumentEncryptedException("The document was encrypted and the provided password was neither the user or owner password.", encryptionDictionary); throw new PdfDocumentEncryptedException("The document was encrypted and the provided password was neither the user or owner password.", encryptionDictionary);
@@ -277,12 +277,15 @@
Array.Copy(encryptionDictionary.OwnerBytes, ownerHash, ownerHash.Length); Array.Copy(encryptionDictionary.OwnerBytes, ownerHash, ownerHash.Length);
Array.Copy(encryptionDictionary.OwnerBytes, ownerHash.Length, validationSalt, 0, validationSalt.Length); Array.Copy(encryptionDictionary.OwnerBytes, ownerHash.Length, validationSalt, 0, validationSalt.Length);
byte[] result;
if (encryptionDictionary.Revision == 6) if (encryptionDictionary.Revision == 6)
{ {
throw new PdfDocumentEncryptedException($"Support for revision 6 encryption not implemented: {encryptionDictionary}."); result = ComputeStupidIsoHash(truncatedPassword, validationSalt, encryptionDictionary.UserBytes);
}
else
{
result = ComputeSha256Hash(truncatedPassword, validationSalt, encryptionDictionary.UserBytes);
} }
var result = ComputeSha256Hash(truncatedPassword, validationSalt);
return result.SequenceEqual(ownerHash); return result.SequenceEqual(ownerHash);
} }
@@ -571,36 +574,53 @@
// Truncate the UTF-8 representation of the password to 127 bytes if it is longer than 127 bytes // Truncate the UTF-8 representation of the password to 127 bytes if it is longer than 127 bytes
password = TruncatePasswordTo127Bytes(password); password = TruncatePasswordTo127Bytes(password);
byte[] intermediateKey;
byte[] encryptedFileKey;
// If the password is the owner password: // If the password is the owner password:
// Compute an intermediate owner key by computing the SHA-256 hash of the UTF-8 password concatenated with the 8 bytes of owner Key Salt, // Compute an intermediate owner key by computing the SHA-256 hash of the UTF-8 password concatenated with the 8 bytes of owner Key Salt,
// concatenated with the 48-byte U string. The 32-byte result is the key used to decrypt the 32-byte OE string using AES-256 in CBC mode // concatenated with the 48-byte U string. The 32-byte result is the key used to decrypt the 32-byte OE string using AES-256 in CBC mode
// with no padding and an initialization vector of zero. The 32-byte result is the file encryption key. // with no padding and an initialization vector of zero. The 32-byte result is the file encryption key.
if (!isUserPassword) if (!isUserPassword)
{ {
throw new PdfDocumentEncryptedException($"Unsupported owner key encryption with revision: {encryptionDictionary.Revision}."); var ownerKeySalt = new byte[8];
} Array.Copy(encryptionDictionary.OwnerBytes, 40, ownerKeySalt, 0, ownerKeySalt.Length);
// If the password is the user password: if (encryptionDictionary.Revision == 6)
// Compute an intermediate user key by computing the SHA-256 hash of the UTF-8 password concatenated with the 8 bytes of user Key Salt. {
// The 32-byte result is the key used to decrypt the 32-byte UE string using AES-256 in CBC mode with no padding and an initialization vector of zero. intermediateKey = ComputeStupidIsoHash(password, ownerKeySalt, encryptionDictionary.UserBytes);
// The 32-byte result is the file encryption key. }
var userKeySalt = new byte[8]; else
Array.Copy(encryptionDictionary.UserBytes, 40, userKeySalt, 0, 8); {
intermediateKey = ComputeSha256Hash(password, ownerKeySalt, encryptionDictionary.UserBytes);
}
byte[] intermediateKey; encryptedFileKey = encryptionDictionary.OwnerEncryptionBytes;
if (encryptionDictionary.Revision == 6)
{
intermediateKey = ComputeStupidIsoHash(password, userKeySalt, null);
} }
else else
{ {
intermediateKey = ComputeSha256Hash(password, userKeySalt); // If the password is the user password:
// Compute an intermediate user key by computing the SHA-256 hash of the UTF-8 password concatenated with the 8 bytes of user Key Salt.
// The 32-byte result is the key used to decrypt the 32-byte UE string using AES-256 in CBC mode with no padding and an initialization vector of zero.
// The 32-byte result is the file encryption key.
var userKeySalt = new byte[8];
Array.Copy(encryptionDictionary.UserBytes, 40, userKeySalt, 0, 8);
if (encryptionDictionary.Revision == 6)
{
intermediateKey = ComputeStupidIsoHash(password, userKeySalt, null);
}
else
{
intermediateKey = ComputeSha256Hash(password, userKeySalt);
}
encryptedFileKey = encryptionDictionary.UserEncryptionBytes;
} }
var iv = new byte[16]; var iv = new byte[16];
using (var rijndaelManaged = new RijndaelManaged { Key = intermediateKey, IV = iv, Mode = CipherMode.CBC, Padding = PaddingMode.None }) using (var rijndaelManaged = new RijndaelManaged { Key = intermediateKey, IV = iv, Mode = CipherMode.CBC, Padding = PaddingMode.None })
using (var memoryStream = new MemoryStream(encryptionDictionary.UserEncryptionBytes)) using (var memoryStream = new MemoryStream(encryptedFileKey))
using (var output = new MemoryStream()) using (var output = new MemoryStream())
using (var cryptoStream = new CryptoStream(memoryStream, rijndaelManaged.CreateDecryptor(intermediateKey, iv), CryptoStreamMode.Read)) using (var cryptoStream = new CryptoStream(memoryStream, rijndaelManaged.CreateDecryptor(intermediateKey, iv), CryptoStreamMode.Read))
{ {