2G Hacking

A5/1 Encryption Breaking

A5/1 is the encryption algorithm used in 2G GSM networks. Due to its weak 64-bit key and known vulnerabilities, it can be broken in real-time to decrypt voice calls and SMS messages.

Critical Security Vulnerability

The A5/1 stream cipher was designed in 1987 and has been cryptographically broken. Using rainbow tables and modern computing power, attackers can decrypt A5/1 encrypted communications in seconds. The attack requires capturing the encrypted traffic and the initial keystream.

Attack Flow Diagram

Step-by-step visualization of the attack process

Impact

Complete decryption of voice calls
SMS message interception and decryption
Loss of communication confidentiality
Exposure of sensitive personal and business information
Compliance violations for regulated industries

Attack Vectors

Capture encrypted GSM traffic using SDR
Use rainbow tables to crack A5/1 encryption
Real-time decryption with sufficient computing power
Passive monitoring without detection
Targeted surveillance of specific subscribers

Attack Methodology

1Set up SDR to capture GSM traffic on target frequencies
2Identify target device by IMSI or TMSI
3Capture encrypted voice or SMS traffic
4Extract keystream from captured data
5Use Kraken or similar tools with rainbow tables
6Decrypt communications in near real-time

Mitigation Strategies

Upgrade to 3G/4G networks with stronger encryption
Disable 2G on devices when not needed
Use end-to-end encrypted communication apps
Implement A5/3 encryption where 2G is necessary
Monitor for forced 2G downgrade attacks
Deploy network-level encryption for sensitive communications

Real-World Examples

•Karsten Nohl's demonstration of A5/1 cracking at CCC
•Intelligence agency surveillance programs
•Criminal interception of business communications
•Privacy violations in countries with weak telecom regulations

Related Attacks

IMSI Catching

IMSI catchers are rogue base stations that trick mobile devices into connecting to them, allowing attackers to capture International Mobile Subscriber Identity (IMSI) numbers and intercept communications.

Fake BTS Attacks

Fake Base Transceiver Station (BTS) attacks involve deploying rogue cell towers that impersonate legitimate network infrastructure to intercept communications and perform man-in-the-middle attacks.

Downgrade Attacks

Downgrade attacks force mobile devices to connect to older, less secure network technologies (2G) where encryption is weaker and easier to break, enabling various attack vectors.

References