IDEA Encryption & Decryption

IDEA (International Data Encryption Algorithm) is a symmetric-key block cipher designed by Xuejia Lai and James Massey of ETH Zurich in 1991. It was intended as a replacement for the Data Encryption Standard (DES).

IDEA uses a 128-bit key to encrypt 64-bit blocks through 8.5 rounds of a complex algorithm based on mixing operations from different algebraic groups: XOR, addition modulo 2^16, and multiplication modulo 2^16+1.

Key Features

• 128-bit fixed key length provides strong security
• 64-bit block size for data processing
• 8.5 rounds of encryption for thorough mixing
• Patent-free since 2012, freely usable worldwide

Encryption Modes

• CBC: Cipher Block Chaining - Each block is XORed with the previous ciphertext block before encryption. Requires IV.
• ECB: Electronic Codebook - Each block is encrypted independently. Simple but not recommended for most uses.
• CFB: Cipher Feedback - Turns block cipher into stream cipher. Self-synchronizing mode.
• OFB: Output Feedback - Generates keystream independently. No error propagation.
• RAW: Raw Block - Direct single block encryption without any chaining mode. No IV required.

Security Considerations

• 128-bit key provides adequate security against brute force attacks
• No practical attacks have been found against full 8.5-round IDEA
• 64-bit block size is considered small by modern standards
• For new applications, AES is recommended as the modern standard

Use Cases

• Legacy system compatibility and maintenance
• PGP (Pretty Good Privacy) implementations
• Educational purposes and cryptography studies
• Historical cryptographic research and analysis

References

• Wikipedia - International Data Encryption Algorithm
• Original IDEA Paper by Lai and Massey