3DS ReferenceProtocol & field guide

EMV 3-D Secure · Core specification 2.3.1.1

ACS Counter ACS to SDKacsCounterAtoS

ACS Counter ACS to SDK in Challenge Response (CRes).

Source edition: Core 2.3.1.1 · Type: String · Length: 3 characters · Minimum length: 3 · Maximum length: 3

Baseline in CRes Required

Varies by context. Requirement or applicability varies by channel or message category. Select a specific context to resolve it. Usage and conditions ↓

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Usage in CRes

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.

Format and scope

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

Source components: ACS. Channels: 01-APP. Categories: 01-PA, 02-NPA.

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

Related FAQ 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)

Transaction context

This reference covers the published source edition. Use the explorer to inspect this field and any applicable transaction conditions. Scheme programme requirements are not inferred from the protocol edition.

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Sources and related references

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.

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