Android Full Disk Encryption

[Sc00bz]

If you decrypt the second AES block in the superblock, then you can test the following which gets you around 1 in 2 ^ 92.3:

Code:

Offset (bytes) | Size (bytes) | Description ---------------+--------------+--------------------- 1040 | 4 | s_free_inodes_count 1044 | 4 | s_first_data_block 1048 | 4 | s_log_block_size 1052 | 4 | s_log_frag_size

Code:

// exact: s_first_data_block == 0 || (s_first_data_block == 1 && s_log_block_size == 0) if ((unsigned int) s_first_data_block < 2) // assumes max block size is 32MiB if ((unsigned int) s_log_block_size < 16) // assumes max fragment size is 32MiB and (min is 1 byte) if ((int) s_log_frag_size >= -10 && (int) s_log_frag_size < 16) // volume_size_KiB is 32 bit if the volume is less than 4 TiB if ((unsigned int) s_free_inodes_count < volume_size_KiB >> s_log_block_size)

Also I think s_free_inodes_count is signed so that gives you another bits worth of validation.