Skipjack Encryption

Skipjack is a block cipher developed by the U.S. National Security Agency (NSA) for use in the Clipper chip.

Key Generation

Generate a secure key and initialization vector (IV) for Skipjack encryption

Encrypt File

Upload a file and encrypt it with Skipjack

Decrypt File

Upload an encrypted file and decrypt it with Skipjack

About Skipjack Encryption

Skipjack is a block cipher developed by the U.S. National Security Agency (NSA) and was declassified in 1998. It was originally designed for use in the Clipper chip as part of the controversial Clipper encryption program in the 1990s.

Key Features:
  • Block Size: 64 bits
  • Key Size: 80 bits
  • Rounds: 32 rounds
  • Structure: Unbalanced Feistel network
  • Operations: Uses simple operations like table lookups, permutations, and XORs
How Skipjack Works:

Skipjack uses two different rule types, called "Rule A" and "Rule B", which are applied in a specific pattern:

  1. The 64-bit block is divided into four 16-bit words.
  2. The algorithm applies 8 rounds of Rule A, followed by 8 rounds of Rule B, followed by 8 more rounds of Rule A, and finally 8 more rounds of Rule B.
  3. Rule A performs a permutation on one word and then combines it with other words using XOR operations.
  4. Rule B performs a different permutation and combination pattern.
  5. Both rules use an F-table (a fixed substitution box) and the key schedule to introduce non-linearity.
Historical Context:
  • Clipper Chip: Skipjack was designed for the Clipper chip, which was part of a U.S. government initiative to create a standard encryption device with a built-in backdoor for law enforcement (key escrow).
  • Controversy: The Clipper chip program was highly controversial due to privacy concerns and was eventually abandoned.
  • Declassification: Skipjack was declassified in 1998, allowing cryptographers to analyze its design.
Security Assessment:
  • Cryptanalysis: After declassification, Skipjack was analyzed by the cryptographic community. The best known attack requires 2^31 chosen plaintexts and 2^71 operations, which is still impractical.
  • Key Size: The 80-bit key size is considered too small by modern standards, making it vulnerable to brute force attacks with sufficient computing power.
  • Design Principles: Despite being designed by the NSA, no deliberate weaknesses or backdoors have been found in the algorithm itself (separate from the key escrow system of the Clipper chip).
Current Status:

Skipjack is primarily of historical interest today. It is not widely used in modern cryptographic applications due to:

  • Its relatively small key size (80 bits)
  • The availability of more thoroughly analyzed and standardized algorithms like AES
  • Its association with the controversial Clipper chip program
Note: While Skipjack itself is not considered insecure (apart from its key size), modern applications should use more widely vetted algorithms like AES for sensitive data encryption.