Fix: ASN.1 Choice Wrapping

src/lib/certificates.legacy.test.ts

@@ -0,0 +1,77 @@
+import { test, expect } from 'vitest';
+import * as Certificates from './certificates.js';
+import * as KeetaNetClient from '@keetanetwork/keetanet-client';
+
+/*
+ * Backward-compatibility regression: this certificate was signed before CHOICE
+ * fields gained the positional context-tag wrapper, so entityType's schemeName
+ * is encoded bare while its sibling id stays context-tagged. Signed with the
+ * seed below (ED25519) and
+ * entityType { person: [{ id: '123-45-6789', schemeName: 'SSN' }] }.
+ */
+const legacySeed = 'B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0B0';
+
+const legacyCertPEM = `-----BEGIN CERTIFICATE-----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+lsu19v08zYrgSb1IS7lKmCEQXRzZ+AYJYIZIAWUDBAIIBCBoNEZJxtieIXV1zgVZ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+-----END CERTIFICATE-----`;
+
+test('legacy bare-CHOICE entityType still decodes', async function() {
+	const account = KeetaNetClient.lib.Account.fromSeed(legacySeed, 1, KeetaNetClient.lib.Account.AccountKeyAlgorithm.ED25519);
+	const certificate = new Certificates.Certificate(legacyCertPEM, { subjectKey: account, moment: null });
+
+	const entityType = await certificate.getAttributeValue('entityType');
+	expect(entityType.person?.[0]?.schemeName, 'bare CHOICE schemeName decodes').toBe('SSN');
+	expect(entityType.person?.[0]?.id, 'context-tagged sibling id decodes').toBe('123-45-6789');
+});

src/lib/certificates.ts

@@ -293,6 +293,69 @@
 	return(schema);
 }
 
+/**
+ * Determine whether a schema node is an ASN.1 CHOICE.
+ */
+function isChoiceSchema(schema: ASN1.Schema): boolean {
+	return(typeof schema === 'object' && schema !== null && 'choice' in schema);
+}
+
+/**
+ * Produce a legacy-compatible schema in which CHOICE fields are encoded without
+ * the positional context-tag wrapper that newer certificates add.
+ */
+function toLegacyChoiceSchema(schema: ASN1.Schema): ASN1.Schema {
+	if (typeof schema !== 'object' || schema === null) {
+		return(schema);
+	}
+	if (Array.isArray(schema)) {
+		// eslint-disable-next-line @typescript-eslint/consistent-type-assertions
+		return(schema.map(toLegacyChoiceSchema) as unknown as ASN1.Schema);
+	}
+
+	if ('choice' in schema) {
+		if (Array.isArray(schema.choice)) {
+			return({ choice: schema.choice.map(toLegacyChoiceSchema) });
+		}
+
+		const mappedChoice: { [key: string]: ASN1.Schema } = {};
+		for (const [key, value] of Object.entries(schema.choice)) {
+			mappedChoice[key] = toLegacyChoiceSchema(value);
+		}
+
+		return({ choice: mappedChoice });
+	}
+
+	if ('sequenceOf' in schema) {
+		return({ sequenceOf: toLegacyChoiceSchema(schema.sequenceOf) });
+	}
+	if ('optional' in schema) {
+		return({ optional: toLegacyChoiceSchema(schema.optional) });
+	}
+	if ('type' in schema && schema.type === 'context') {
+		// Strip the positional wrapper when it wraps a CHOICE to restore the bare form
+		if (isChoiceSchema(schema.contains)) {
+			return(toLegacyChoiceSchema(schema.contains));
+		}
+
+		return({ ...schema, contains: toLegacyChoiceSchema(schema.contains) });
+	}
+	if ('type' in schema && schema.type === 'struct') {
+		const legacyContains: { [key: string]: ASN1.Schema } = {};
+		for (const [fieldName, fieldSchema] of Object.entries(schema.contains)) {
+			legacyContains[fieldName] = toLegacyChoiceSchema(fieldSchema);
+		}
+
+		return({
+			type: 'struct',
+			fieldNames: schema.fieldNames,
+			contains: legacyContains
+		});
+	}
+
+	return(schema);
+}
+
 /**
  * Fallback decoder for entityType attribute from old certificates.
  * Transforms raw ASN1 into the expected EntityType structure.
@@ -375,22 +438,37 @@
 		// @ts-expect-error
 		decodedASN1 = new ASN1.BufferStorageASN1(value, schema).getASN1();
 	} catch (firstError) {
-		// Fallback: try with backwards-compatible schema (context tags stripped)
-		// This supports old certificates encoded before context tags were added
+		/*
+		 * Certificates signed before CHOICE fields gained their positional wrapper
+		 * encode those fields bare; retry with the pre-wrapper schema
+		 */
 		try {
-			// Special handling for entityType
-			if (name === 'entityType') {
-				const candidate = decodeEntityTypeFallback(value, principals);
-				return(asAttributeValue(name, candidate));
-			}
-
-			const backwardsCompatSchema = unwrapContextTagsFromSchema(schema);
+			const legacyChoiceSchema = toLegacyChoiceSchema(schema);
 			// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
-			decodedASN1 = new ASN1.BufferStorageASN1(value, backwardsCompatSchema).getASN1();
-			usedSchema = backwardsCompatSchema;
+			decodedASN1 = new ASN1.BufferStorageASN1(value, legacyChoiceSchema).getASN1();
+			usedSchema = legacyChoiceSchema;
 		} catch {
-			// If both fail, throw the original error
-			throw(firstError);
+			/*
+			 * Fallback: try with backwards-compatible schema (context tags stripped)
+			 * This supports old certificates encoded before context tags were added
+			 */
+			try {
+				/*
+				 * Special handling for entityType
+				 */
+				if (name === 'entityType') {
+					const candidate = decodeEntityTypeFallback(value, principals);
+					return(asAttributeValue(name, candidate));
+				}
+
+				const backwardsCompatSchema = unwrapContextTagsFromSchema(schema);
+				// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+				decodedASN1 = new ASN1.BufferStorageASN1(value, backwardsCompatSchema).getASN1();
+				usedSchema = backwardsCompatSchema;
+			} catch {
+				// If both fail, throw the original error
+				throw(firstError);
+			}
 		}
 	}
 

src/services/kyc/utils/generate-kyc-schema.ts

@@ -478,8 +478,13 @@ function genSequenceSchema(typeName: string, fields: { [key: string]: { type: st
 
 		const baseSchema = fieldInfo.schema;
 		const isOptional = fieldInfo.optional;
-		const isChoiceField = fieldInfo.isChoice;
-		if (hasAnyOptionalField && !isChoiceField) {
+		/*
+		 * CHOICE fields are wrapped in a positional context tag just like every
+		 * other field. Leaving them bare lets a CHOICE alternative's own context
+		 * tag collide with a sibling field's positional tag, which makes the
+		 * SEQUENCE ambiguous to a tag-driven decoder.
+		 */
+		if (hasAnyOptionalField) {
 			const wrappedInContext = `{ type: 'context', kind: 'explicit', value: ${index}, contains: ${baseSchema} }`;
 			if (isOptional) {
 				return(`\t\t${fname}: { optional: ${wrappedInContext} }`);