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<?php |
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/* |
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* This file is part of the PHP EcryptFS library. |
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* (c) 2017 by Dennis Birkholz |
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* All rights reserved. |
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* For the license to use this library, see the provided LICENSE file. |
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*/ |
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namespace Iqb\Ecryptfs; |
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/** |
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* The FileHeader class represents the metadata stored at the beginning of each encrypted file. |
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* It marks the file as a valid EcryptFS encrypted file (via the Magic Marker) and |
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* contains information about the real file size of the encrypted file, the key to decrypt the file, |
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* the method used for encrypting the file, etc. |
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*/ |
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class FileHeader |
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{ |
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/** |
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* Default file header size |
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* |
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* @link https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/fs/ecryptfs/ecryptfs_kernel.h?h=v4.11.3#n45 |
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*/ |
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const MINIMUM_HEADER_EXTENT_SIZE = 8192; |
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/** |
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* Default block size |
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* |
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* @link https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/fs/ecryptfs/ecryptfs_kernel.h?h=v4.11.3#n44 |
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*/ |
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const DEFAULT_EXTENT_SIZE = 4096; |
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/** |
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* Magic marker to detect if a file is a valid EcryptFS file |
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* |
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* @link https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/fs/ecryptfs/ecryptfs_kernel.h?h=v4.11.3#n130 |
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*/ |
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const MAGIC_MARKER = 0x3c81b7f5; |
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/** |
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* Size of the unencrypted file |
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* |
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* @var int |
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*/ |
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public $size; |
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/** |
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* @var int |
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*/ |
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public $version; |
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/** |
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* @var int |
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*/ |
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public $flags; |
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/** |
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* @var int |
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*/ |
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public $extentSize; |
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/** |
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* @var int |
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*/ |
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public $extentsAtFront; |
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/** |
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* @var int |
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*/ |
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public $metadataSize; |
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/** |
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* @var int |
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*/ |
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public $cipherCode; |
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/** |
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* Encrypted file encryption key (FEK), encrypted with the FEKEK |
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* |
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* @var string |
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*/ |
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public $encryptedFileKey; |
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/** |
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* Decrypted file encryption key (FEK) |
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* |
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* @var string |
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*/ |
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public $fileKey; |
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/** |
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* Root initialisation vector, used to calculate IV for each block. |
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* |
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* @var string |
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*/ |
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public $rootIv; |
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public static function parse($fileHandle) : self |
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{ |
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if (!\is_resource($fileHandle)) { |
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throw new \InvalidArgumentException('Parameter $fileHandle must be an open file handle.'); |
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} |
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$headerData = \stream_get_contents($fileHandle, self::MINIMUM_HEADER_EXTENT_SIZE); |
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if (\strlen($headerData) < self::MINIMUM_HEADER_EXTENT_SIZE) { |
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throw new \RuntimeException('Could not read enough data to parse header.'); |
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} |
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$headerValues = unpack('Jsize/N2marker/Cversion/sreserved/Cflags/Nextentsize/nextentsatfront', $headerData); |
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$pos = 26; |
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// see https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/fs/ecryptfs/crypto.c?h=v4.11.3#n857 |
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if (($headerValues['marker1'] ^ self::MAGIC_MARKER) !== $headerValues['marker2']) { |
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throw new \DomainException('Invalid magic marker.'); |
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} |
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$header = new self(); |
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$header->size = $headerValues['size']; |
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$header->version = $headerValues['version']; |
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$header->flags = $headerValues['flags']; |
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$header->extentSize = $headerValues['extentsize']; |
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$header->extentsAtFront = $headerValues['extentsatfront']; |
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$header->metadataSize = $header->extentsAtFront * $header->extentSize; |
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// Read remaining header data so stream is positioned at the beginning of the data |
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if ($header->metadataSize > self::MINIMUM_HEADER_EXTENT_SIZE) { |
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$headerData .= \stream_get_contents($fileHandle, ($header->metadataSize - self::MINIMUM_HEADER_EXTENT_SIZE)); |
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} |
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$tag3 = Tag3Packet::parse($headerData, $pos); |
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$header->cipherCode = $tag3->cipherCode; |
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$header->encryptedFileKey = $tag3->encryptedKey; |
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if (!\in_array(\strlen($header->encryptedFileKey), CryptoEngineInterface::CIPHER_KEY_SIZES[$header->cipherCode])) { |
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throw new \RuntimeException(\sprintf("Invalid key size (%u bit) for cipher 0x%x detected, file header may be corrupt!", \strlen($header->encryptedFileKey)*8, $header->cipherCode)); |
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} |
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return $header; |
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} |
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/** |
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* Decrypt the file encryption key (FEK) using the file encryption key encryption key (FEKEK). |
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* The cipher method for FEK encryption and for file contents encryption is encoded in the header. |
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* The cipher key size for FEK encryption is the same as for file contents encryption so |
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* the same number of bytes from the FEKEK is uses as bytes for the FEK exist. |
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* |
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* @param CryptoEngineInterface $cryptoEngine |
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* @param string $fekek |
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*/ |
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public function decryptFileKey(CryptoEngineInterface $cryptoEngine, string $fekek) |
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{ |
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$cipherKeySize = \strlen($this->encryptedFileKey); |
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if (\strlen($fekek) < $cipherKeySize) { |
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throw new \InvalidArgumentException(\sprintf("Decryption requires %u key bytes, supplied FEKEK has only %u bytes!", $cipherKeySize, \strlen($fekek))); |
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} |
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$realFekek = \substr($fekek, 0, $cipherKeySize); |
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$blockSize = $cryptoEngine::CIPHER_BLOCK_SIZES[$this->cipherCode]; |
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$iv = \str_repeat("\0", $blockSize); |
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// Emulate ECB mode here ... |
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$this->fileKey = ''; |
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foreach (\str_split($this->encryptedFileKey, $blockSize) as $block) { |
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$this->fileKey .= $cryptoEngine->decrypt($block, $this->cipherCode, $realFekek, $iv); |
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} |
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$this->rootIv = \hash('md5', $this->fileKey, true); |
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} |
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} |
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iqb /
ecryptfs
