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RAR 格式

文件格式

RAR 文件主要由标记块,压缩文件头块,文件头块,结尾块组成。

其每一块大致分为以下几个字段:

名称 大小 描述
HEAD_CRC 2 全部块或块部分的CRC
HEAD_TYPE 1 块类型
HEAD_FLAGS 2 阻止标志
HEAD_SIZE 2 块大小
ADD_SIZE 4 可选字段 - 添加块大小

Rar压缩包的文件头为 0x 52 61 72 21 1A 07 00

紧跟着文件头(0x526172211A0700)的是标记块(MARK_HEAD),其后还有文件头(File Header)。

名称 大小 描述
HEAD_CRC 2 CRC of fields from HEAD_TYPE to FILEATTR and file name
HEAD_TYPE 1 Header Type: 0x74
HEAD_FLAGS 2 Bit Flags (Please see ‘Bit Flags for File in Archive’ table for all possibilities)(伪加密)
HEAD_SIZE 2 File header full size including file name and comments
PACK_SIZE 4 Compressed file size
UNP_SIZE 4 Uncompressed file size
HOST_OS 1 Operating system used for archiving (See the ‘Operating System Indicators’ table for the flags used)
FILE_CRC 4 File CRC
FTIME 4 Date and time in standard MS DOS format
UNP_VER 1 RAR version needed to extract file (Version number is encoded as 10 * Major version + minor version.)
METHOD 1 Packing method (Please see ‘Packing Method’ table for all possibilities
NAME_SIZE 2 File name size
ATTR 4 File attributes
HIGH_PACK_SIZ 4 High 4 bytes of 64-bit value of compressed file size. Optional value, presents only if bit 0x100 in HEAD_FLAGS is set.
HIGH_UNP_SIZE 4 High 4 bytes of 64-bit value of uncompressed file size. Optional value, presents only if bit 0x100 in HEAD_FLAGS is set.
FILE_NAME NAME_SIZE bytes File name - string of NAME_SIZE bytes size
SALT 8 present if (HEAD_FLAGS & 0x400) != 0
EXT_TIME variable size present if (HEAD_FLAGS & 0x1000) != 0

每个 RAR 文件的结尾快(Terminator)都是固定的。

Field Name Size (bytes) Possibilities
HEAD_CRC 2 Always 0x3DC4
HEAD_TYPE 1 Header type: 0x7b
HEAD_FLAGS 2 Always 0x4000
HEAD_SIZE 2 Block size = 0x0007

更多详见 http://www.forensicswiki.org/wiki/RAR

主要攻击

爆破

伪加密

RAR 文件的伪加密在文件头中的位标记字段上,用 010 Editor 可以很清楚的看见这一位,修改这一位可以造成伪加密。

其余明文攻击等手法依旧同 ZIP 中介绍的一样。