DES Key Schedule

Generate subkeys K₁ and K₂

Mission tie-in: DES Feistel Round traced one round using K₁. This lesson shows how K₁ and K₂ are derived from the 64-bit key.

Pipeline

64-bit K → PC-1 → C₀ ‖ D₀28+28 bits → Left shifts → PC-2 → Kₙ
PC-1: Drop parity bits (8,16,…,64) → 56 effective bits.
Split: C₀ (28 bits) ‖ D₀ (28 bits).
Shift schedule: Rounds 1,2,9,16 → 1 left shift; all others → 2 shifts (rotate left).
PC-2: Select 48 bits from CₙDₙ → subkey Kₙ.

Worked example — Key = 133457799BBCDFF1

Subkeys K₁ and K₂ from FIPS PC-1 → left shifts → PC-2 (Grabbe / Stallings Ch.3).

Use K₁ in DES Feistel Round f-function trace.

Retrieval practice

After PC-1, what is DES effective key length?

Stuck? Ask: "Generate K₃ from this key" or "Why shift 1 vs 2?"