Why? #

What This Fork Fixes #

The original app_device_integrity had a critical issue:

• The challengeString (nonce) sent from Flutter was completely ignored.

• The plugin always used a static Base64.encode(ByteArray(40)) value.

• This produced the well-known "AAAAAAAAAAAA..." nonce in Play Integrity logs.

• Real server-side verification was not possible because the nonce never matched.

Fixes in This Version #

This fork fixes all of that.

• Proper nonce passthrough from Flutter → Native → Play Integrity

• Removed static dummy nonce (ByteArray(40))

• Added proper MethodChannel argument handling

• Updated API to accept challengeString exactly as given

• Real attestation with server-side validation now works

• README rewritten for clarity

• Additional flow diagram for easier understanding

🚀 How to Use #

1. Request nonce from your backend

Your server must generate a unique challenge per session.

final sessionId = await api.getNonce();

2. Pass nonce into the plugin

final integrity = AppDeviceIntegrityPlus();

if (Platform.isAndroid) {
  final token = await integrity.getAttestationServiceSupport(
    challengeString: sessionId,
    gcp: 523725941100,
  );
} else {
  final token = await integrity.getAttestationServiceSupport(
    challengeString: sessionId,
  );
}

3. Send token to backend for validation

await api.verifyIntegrity(token);

📊 Attestation Flow (App ↔ API Server ↔ Google) #

sequenceDiagram
    participant APP
    participant API as API Server
    participant GOOGLE as Google Server (Play Integrity)

    APP->>API: Request requestHash (based on request data)
    API-->>APP: Generate & return requestHash

    note right of APP: Play Integrity preparation (prepare phase)

    APP->>GOOGLE: prepareIntegrityToken(cloudProjectNumber)
    GOOGLE-->>APP: Return IntegrityTokenProvider

    note right of APP: Standard request can now be executed

    APP->>GOOGLE: provider.request(requestHash included)
    GOOGLE-->>APP: Return Standard signed token (JWT)

    APP->>API: Send token to server for verification

    API->>GOOGLE: Validate & decrypt token
    GOOGLE->>API: Return token payload (including requestHash)

    note left of API: Compare requestHash with original

    API-->>APP: OK (valid client) or Error (tampered/replay attack)

📚 References #

• https://developer.android.com/google/play/integrity/standard?hl=ko#java
• https://developer.android.com/google/play/integrity/overview?hl=ko

🔧 왜 만들게 되었는가? #

원본 app_device_integrity 플러그인의 문제 #

• Integrity API의 기존방식 제공(레거시)
• Flutter에서 넘긴 challengeString(nonce)을 전혀 사용하지 않음
• 내부에서 항상 ByteArray(40) → Base64 인코딩한 값 사용
• 그래서 Play Integrity 로그에 "AAAAAAAAAA..." nonce만 출력됨
• 서버 검증 시 nonce 불일치 → 정상적인 보안 검증 불가능

✅ 이 버전에서 수정 / 개선된 내용 #

• Integrity API의 표준 방식으로 리펙터링

• 서버에서 받은 nonce를 그대로 Play Integrity에 전달

• 더 이상 static dummy nonce 사용하지 않음

• MethodChannel 파라미터 처리 수정

• Android/iOS에서 실제 nonce 기반 토큰 생성 가능

• README 전면 재작성

• 플로우 다이어그램 추가
  

🚀 사용 방법 #

1. 서버에서 nonce 발급

final sessionId = await api.getNonce();

2. 플러그인에 nonce 전달

final integrity = AppDeviceIntegrityPlus();

if (Platform.isAndroid) {
  final token = await integrity.getAttestationServiceSupport(
    challengeString: sessionId,
    gcp: 523725941100,
  );
} else {
  final token = await integrity.getAttestationServiceSupport(
    challengeString: sessionId,
  );
}

3. 토큰을 서버로 전달해 검증

await api.verifyIntegrity(token);

📊 전체 플로우 (앱 ↔ 서버 ↔ Google) #

sequenceDiagram
    participant APP
    participant API as API Server
    participant GOOGLE as Google Server
    
    APP->>API: requestHash 요청 (요청 데이터 기반)
    API-->>APP: requestHash 생성 & 발급

    note right of APP: 앱 내부에서 Play Integrity 준비(prepare)

    APP->>GOOGLE: prepareIntegrityToken(cloudProjectNumber)
    GOOGLE-->>APP: IntegrityTokenProvider 반환

    note right of APP: 이제 표준 요청(request) 가능

    APP->>GOOGLE: provider.request(requestHash 포함)
    GOOGLE-->>APP: Standard signed token 반환

    APP->>API: token 전달 (검증 요청)

    API->>GOOGLE: 복호화 및 토큰 검증
    GOOGLE->>API: requestHash 반환

    API-->>APP: OK (정상) 또는 Error (위변조/재전송 공격)
    note left of API: requestHash 대조

📚 참고 #

• https://developer.android.com/google/play/integrity/standard?hl=ko#java
• https://developer.android.com/google/play/integrity/overview?hl=ko