Information disclosure due to RC2 cipher usage in PyCryptodome

High Risk Cryptographic Vulnerabilities
pythoncryptographypycryptodomeencryptioninformation-disclosure

What it is

Using the RC2 cipher algorithm exposes applications to information disclosure vulnerabilities. RC2 is an obsolete cipher that lacks modern security properties and is vulnerable to practical cryptanalysis. Attackers can potentially decrypt sensitive data or recover plaintext from ciphertext encrypted with RC2.

ℹī¸ Configuration Fix

Configuration changes required - see explanation below.

💡 Explanation

ℹī¸ Configuration Fix

Configuration changes required - see explanation below.

💡 Explanation

ℹī¸ Configuration Fix

Configuration changes required - see explanation below.

💡 Explanation

Why it happens

Code uses RC2: from Crypto.Cipher import ARC2; cipher = ARC2.new(key, ARC2.MODE_CBC). RC2 is obsolete cipher from 1987. Variable key size but weak algorithm. Vulnerable to related-key attacks. 64-bit block size like Blowfish. No legitimate modern use case.

Root causes

Using RC2 Cipher from PyCryptodome

Code uses RC2: from Crypto.Cipher import ARC2; cipher = ARC2.new(key, ARC2.MODE_CBC). RC2 is obsolete cipher from 1987. Variable key size but weak algorithm. Vulnerable to related-key attacks. 64-bit block size like Blowfish. No legitimate modern use case.

Legacy PKCS#12 or S/MIME Systems Using RC2

Old certificate systems with RC2. PKCS#12 files historically using RC2 by default. S/MIME encryption with RC2. Legacy interoperability requirements. Export regulations historically favored RC2. Backward compatibility with ancient systems. Modern implementations should reject RC2.

Using RC2 for Legacy System Interoperability

Communicating with old applications requiring RC2. Mainframe integration. Legacy hardware encryption. Third-party systems not updated. Vendor lock-in with RC2. Interoperability forcing weak cipher usage. Compatibility shouldn't override security for critical applications.

Choosing RC2 Due to Export Restriction History

Historical export control compliance using RC2. Outdated compliance requirements. RC2 allowed for export when strong ciphers restricted. Export regulations relaxed but code unchanged. Historical constraints no longer applicable. RC2 unnecessary in modern international applications.

RC2 in Embedded or Resource-Constrained Systems

Using RC2 for perceived simplicity. Low-resource embedded systems. Microcontroller encryption. Believing RC2 sufficient for constrained environments. Modern lightweight ciphers like ChaCha20 better alternatives. Resource constraints don't justify broken ciphers.

Fixes

1

Replace RC2 with AES for All Use Cases

Use AES-256: from Crypto.Cipher import AES; cipher = AES.new(key, AES.MODE_GCM). AES mandatory for modern applications. Supported by all platforms. Hardware acceleration available. NIST approved. No legitimate reason to use RC2. Immediate replacement required.

2

Update Legacy Systems to Modern Cipher Suites

Upgrade systems rejecting RC2. PKCS#12 with AES: use modern tools generating AES-encrypted certificates. S/MIME with AES-256. Update clients and servers. Coordinate migration. Phase out RC2 support completely. Security over backward compatibility.

3

Use ChaCha20-Poly1305 for Resource-Constrained Devices

Lightweight modern cipher: from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305; chacha = ChaCha20Poly1305(key); ciphertext = chacha.encrypt(nonce, plaintext, None). Fast in software. No hardware requirements. Authenticated encryption. Better than RC2 for embedded systems.

4

Reject RC2 in TLS/SSL Configuration

Disable RC2 in SSL contexts: import ssl; context = ssl.create_default_context(); context.set_ciphers('HIGH:!RC2:!aNULL'). Explicitly exclude RC2 from cipher suites. Server and client configuration. Prevent negotiation of weak ciphers. Force strong cipher usage.

5

Implement Cipher Suite Validation and Monitoring

Audit active cipher usage: log cipher selections. Alert on weak cipher detection. Automated tests checking for RC2. Static analysis scanning for insecure algorithms. Runtime monitoring of cryptographic operations. Proactive detection and prevention of weak cipher usage.

6

Remove RC2 Support Entirely from Codebase

Find and remove RC2: grep -r 'ARC2\|RC2' --include="*.py". Delete RC2 code paths. Remove from dependencies if possible. Update documentation forbidding RC2. Security policy explicitly prohibiting obsolete ciphers. Complete elimination prevents future misuse.

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