Android Backup Hash

Technical details, regex signatures, and cracking commands for the Android Backup algorithm.

Regex Identification Signature:

                        \$ab\$[0-9]{1}\*[0-9]{1}\*[0-9]{1,6}\*[a-f0-9]{128}\*[a-f0-9]{128}\*[a-f0-9]{32}\*[a-f0-9]{192}
                    

Hashcat Command (Mode: 18900):

John the Ripper Command:

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What is Android Backup?

The **Android Backup cryptographic hash format** is a proprietary key derivation and encryption scheme introduced by Google in the mid-2010s as part of the Android Backup Service API (introduced in Android 4.0 Ice Cream Sandwich). This format is designed to securely encrypt user data stored in the Android backup database, ensuring confidentiality during transit and at rest. The scheme combines a **PBKDF2-HMAC-SHA1** key derivation function with a **custom AES-CBC encryption wrapper**, where the user’s passphrase is iterated 4096 times (a relatively low iteration count for its era) with a fixed salt derived from the device’s hardware identifier (IMEI/IMEISV or Android ID). The resulting 256-bit key is then used to encrypt the backup payload using AES-256 in CBC mode, with an IV stored alongside the ciphertext. Unlike traditional Android encryption (which relies on the platform’s full-disk encryption), the Backup format explicitly targets individual app data and media files, prioritizing compatibility with cloud-based backup solutions while maintaining backward compatibility with older Android versions.

The **Android Backup hash format is vulnerable to cracking primarily due to its weak key derivation and cryptographic design choices**. The reliance on **PBKDF2-HMAC-SHA1 with only 4096 iterations** makes it susceptible to brute-force attacks, especially when combined with modern GPU/ASIC hardware like Hashcat or custom FPGA/ASIC accelerators, which can evaluate millions of hashes per second. The absence of a **dynamic salt** (the salt is derived from device-specific identifiers) allows attackers to precompute or reuse hashes across multiple devices, reducing the effective entropy of the key space. Additionally, **SHA1’s collision resistance is now considered broken**, and its use in key derivation introduces unnecessary risk, as modern cryptanalysis (e.g., Lenstra’s algorithm) can exploit weaknesses in the hash function’s output distribution. Finally, the **lack of a key stretch mechanism proportional to computational advancements** (e.g., no adaptive iteration count) renders the scheme obsolete by contemporary standards, making it trivially crackable with dedicated hardware within hours or days, depending on the complexity of the user’s passphrase.

Identifying Android Backup Hashes

Identifying a hash blindly is often difficult because multiple algorithms can output strings of the exact same length. For example, a standard 32-character hexadecimal string could be MD5, NTLM, MD4, or LM. To definitively identify Android Backup, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack Android Backup

If you need to recover the plaintext password for a Android Backup hash during a penetration test or forensics investigation, you must supply the correct module ID to your cracking software. Use the exact commands provided at the top of this page to target the hash successfully.