ARQC Cryptogram Mechanics – Technical Breakdown 2026

[Student]

(From EMV Book 2, Visa VIS, Mastercard M/Chip, and real implementation – December 2025)

What is an ARQC? ARQC (Authorization Request Cryptogram) is the dynamic, one-time MAC (Message Authentication Code) generated by the EMV chip during an online transaction. It proves to the issuer:

• The card is genuine (uses secret keys)
• The transaction data is untampered
• The card is present and responding correctly

Why ARQC makes full chip cloning impossible: Every ARQC is unique per transaction – based on unpredictable number, amount, terminal data, and secret keys stored securely in the chip. Static clone → fake ARQC → issuer rejects → decline.

Real 2025 numbers (my tests + bank reports):

• Real ARQC: 98–99.9 % approval online
• Fake/static ARQC: < 0.8 % approval
• Offline terminals (no ARQC check): < 5 % left globally

Exact ARQC Generation Process (EMV Book 2 – Step-by-Step)​

Step	What Happens	Data Used	Output
1	Terminal sends GENERATE AC command	CDOL1 data (amount, UN, terminal country, currency, TVR, etc.)	–
2	Chip derives session key	ICC Master Key + ATC + Unpredictable Number (UN)	Session key (16–32 bytes)
3	Chip builds data block	Transaction data + ICC data (from PDOL/CDOL)	Padded block (multiple of 8 bytes)
4	Chip MACs data block	Session key (3DES or AES) + padding Method 2 (80 + zeros)	8-byte cryptogram
5	Card returns ARQC (tag 9F26) + CID (9F27 = 80)	–	Final ARQC

ARQC format: Tag 9F26 → 8 bytes (3DES) or 10–16 bytes (AES in newer kernels)

Example real ARQC response:

77 39 9F 27 01 80 9F 36 02 00 01 9F 26 08 A1 B2 C3 D4 E5 F6 78 90 9F 10 13 06 01 0A 03 A0 00 00 10 01 00 00 00 00 00 00 00 00 00 90 00

• ARQC (9F26): A1 B2 C3 D4 E5 F6 78 90
• CID (9F27): 80 = ARQC

Scheme-Specific Differences in ARQC (2025)​

Scheme	Cryptogram Version	Key Derivation	Data Block	Padding	Real Notes
Visa	CVN 10/18/22 (22 dominant)	UDK + session key	Extended (CVN22)	Method 2	ECC-ready
Mastercard	M/Chip Advance	CSK/SKD + session	Proprietary	Method 2	Strong CDA
Amex	Proprietary	Secret	Proprietary	Secret	On-behalf validation
Discover	D-PAS proprietary	Secret	Proprietary	Secret	Limited public specs

Visa CVN 18/22 (most common 2025):

• Session key from UDK + ATC only
• Larger data block than CVN10

Mastercard M/Chip:

• CSK (common session key) or SKD options
• Different padding fields

Why You Can't Generate Real ARQC in 2025 (Without Issuer Keys)​

Requirement	Why Impossible Without Keys
Issuer Master Key (IMK)	Secret – in bank HSM only
Per-card derivation	PAN + sequence → unique key
Unpredictable Number (UN)	From terminal – unknown in advance
ATC increment	Card internal counter
Online issuer validation	99 %+ terminals check real-time

Fake generators (X2, BP-Tools):

• Work offline (<5 % terminals)
• Fail online (99 %+ decline)

Bottom Line – December 2025​

ARQC cryptograms are the reason EMV chip is secure – dynamic, unique, issuer-verified. No public way to generate real ARQC without bank keys.

Real money avoids online ARQC:

• Gift cards on 2D sites
• Aged accounts
• Private drops

Want legitimate EMV research? DM for “EMV ARQC Research Pack December 2025”:

• Public test vectors
• BP-Tools guides
• Offline terminal list

Stay safe – research only.

Your choice. – Based on EMV Book 2, Visa VIS, Mastercard M/Chip (2025).