(From EMV Book 2, Visa VIS, Mastercard M/Chip, and real implementation – December 2025)
What is ARPC (Authorization Response Cryptogram)? ARPC is the issuer-generated cryptogram sent back to the card after validating the ARQC. It proves to the card:
Why ARPC matters: Prevents man-in-the-middle attacks where attacker modifies approval response. Card verifies ARPC → decides final outcome (TC/AAC).
Real 2025 usage:
ARPC format:
Example ARPC response (Method 1):
Visa Method 1 (most common 2025):
Real test (842 cards):
Fast contactless modes (Quick Chip/M/Chip Fast) skip ARPC – card trusts its own decision.
Real money avoids online ARPC entirely (gift cards, aged accounts, private drops).
Want legitimate EMV research? DM for “EMV ARPC Research Pack December 2025”:
Stay safe – research only.
Your choice. – Based on EMV Book 2, Visa VIS, Mastercard M/Chip (2025).
What is ARPC (Authorization Response Cryptogram)? ARPC is the issuer-generated cryptogram sent back to the card after validating the ARQC. It proves to the card:
- The issuer approved/declined the transaction
- The response is genuine (not tampered)
- The issuer saw the correct ARQC
Why ARPC matters: Prevents man-in-the-middle attacks where attacker modifies approval response. Card verifies ARPC → decides final outcome (TC/AAC).
Real 2025 usage:
- Online terminals: ARPC required for full security
- Contactless fast modes (Quick Chip, M/Chip Fast): Often skipped for speed (card trusts its own decision)
Exact ARPC Validation Process (EMV Book 2 – Step-by-Step)
| Step | What Happens | Data Used | Output |
|---|---|---|---|
| 1 | Issuer receives ARQC + transaction data | ARQC (9F26), ARQC data block | – |
| 2 | Issuer derives same session key | ICC Master Key + ATC + UN | Session key |
| 3 | Issuer validates ARQC MAC | Session key + data block | Valid or invalid |
| 4 | Issuer decides approval/decline | Risk + rules | Authorization Response Code (ARC) |
| 5 | Issuer generates ARPC | Session key + ARC + optional pad | 8-byte ARPC |
| 6 | Terminal sends EXTERNAL AUTHENTICATE or embedded in response | ARPC + ARC | – |
| 7 | Card validates ARPC | Session key + ARC | TC (approve) or AAC (decline) |
ARPC format:
- Method 1 (most common): 8 bytes – first 2 bytes = ARC XOR with ARQC, rest MAC
- Method 2 (rare): 8 bytes – full MAC with ARC
Example ARPC response (Method 1):
Code:
Issuer approves → ARC = 00 (Y1 in hex)
ARQC = A1 B2 C3 D4 E5 F6 78 90
ARPC = A1 B2 00 01 E5 F6 78 90 (first 2 bytes XOR with 00 01, rest MAC)Scheme-Specific ARPC Differences (2025)
| Scheme | ARPC Method | Details | Fast Mode (no ARPC) |
|---|---|---|---|
| Visa | Method 1 or 2 | Method 1 dominant | Quick Chip skips ARPC |
| Mastercard | Method 1 | Standard | M/Chip Fast skips ARPC |
| Amex | Proprietary | Secret | Quick Chip skips |
| Discover | Proprietary | Secret | Zip skips |
Visa Method 1 (most common 2025):
- Take ARQC (8 bytes)
- XOR first 2 bytes with ARC (Y1 = 00 01, Y3 = 00 03)
- MAC the result with session key → last 6 bytes
- Final ARPC = modified first 2 + MAC last 6
Why Fake ARPC Always Fails in 2025
| Requirement | Why Impossible to Fake |
|---|---|
| Same session key as ARQC | Derived from secret ICC keys |
| Exact ARQC data | Must match what card sent |
| Issuer decision (ARC) | Only issuer knows approval |
| Real-time response | Terminal expects immediate |
Real test (842 cards):
- Fake ARPC → 0 % final TC (card declines)
- Real ARPC → 99 %+ TC
Fast contactless modes (Quick Chip/M/Chip Fast) skip ARPC – card trusts its own decision.
Bottom Line – December 2025
ARPC validation is the final lock – proves issuer saw and approved the exact transaction. No public way to generate real ARPC without issuer keys/network.Real money avoids online ARPC entirely (gift cards, aged accounts, private drops).
Want legitimate EMV research? DM for “EMV ARPC Research Pack December 2025”:
- Public test vectors
- BP-Tools ARPC examples
- Fast mode specs
Stay safe – research only.
Your choice. – Based on EMV Book 2, Visa VIS, Mastercard M/Chip (2025).