3DS ReferenceProtocol & field guide

EMV 3-D Secure · Core specification 2.3.1.1

ACS Counter ACS to SDKacsCounterAtoS

Counter used as a security measure in the ACS to 3DS SDK secure channel. Note: The counter is the decimal value equivalent of the byte, encoded as a numeric string.

Explore this field with transaction context

Message inclusion

Baseline inclusion. Effective requirements depend on transaction context. Check the field’s conditions and FAQ qualifications; select channel and category in the explorer.

MessageBaseline inclusion
CResRequired

Format and scope

Type: String · Length: 3 characters · Minimum length: 3 · Maximum length: 3

Source components
ACS
Device channels
01-APP
Message categories
01-PA, 02-NPA

Reference notes

  • In cryptographic functions (Section 6.2), coded as 1 byte counting 0-255. In CReq/CRes messages, transmitted as decimal string padded to 3 digits. Example: byte 0x23 (35 decimal) → '035'. — FAQ 20 (EMVCo FAQ)

Version history

Field introduction tag: 2.1.0. Introduction tags are curated metadata, not a full history of changes. Compare versions and understand coverage.

Source and review status

EMV_3DS_CoreSpec_v2.3.1.1_20230530.pdf, Table A.1, PDF pages 201

Source review status: carried-forward. Carried-forward material has not acquired a new verification claim.

Source document fingerprint

EMV_3DS_CoreSpec_v2.3.1.1_20230530.pdf

6fdf0aba3fc1a765f96b74dad4069d1e189969f38f0023647021687daf589d6b

Official EMVCo specifications · Methodology and coverage limits