Android APK签名机制的工作原理、结构差异、安全局限与优势

APK 文件结构：
├── META-INF/
│   ├── MANIFEST.MF          # 所有文件的哈希清单
│   ├── CERT.SF              # MANIFEST.MF 的签名摘要
│   └── CERT.RSA (或 .DSA)   # 开发者证书 + 对 CERT.SF 的签名
├── AndroidManifest.xml
├── classes.dex
├── resources.arsc
└── res/, assets/, lib/, etc.

# 伪代码
for file in apk_entries:
    if file not in META-INF/:
        hash = Base64.encode(sha1(file_content))
        MANIFEST.MF += "Name: $file_path\nSHA1-Digest: $hash\n\n"

# 计算 MANIFEST.MF 的哈希
manifest_hash = Base64.encode(sha1(MANIFEST.MF))

# 构建 CERT.SF
CERT.SF = "SHA1-Digest-Manifest: $manifest_hash\n\n"

for entry in MANIFEST.MF.entries:
    entry_hash = Base64.encode(sha1(entry))
    CERT.SF += "Name: $entry_name\nSHA1-Digest: $entry_hash\n\n"

# 使用 PKCS#7 标准封装
CERT.RSA = PKCS7_Signature {
    content: CERT.SF,
    signature: RSA_Sign(sha1(CERT.SF), private_key),
    certificates: [developer_cert, CA_certs...]
}

[ZIP 条目数据块]
    ↓
[APK 签名块] ← 新增区域
    ↓
[ZIP 中央目录]
    ↓
[ZIP 文件结尾 (EOCD)]

[块大小] (8字节)
[ID-Value 对列表]
[块大小] (重复，用于快速定位)

// 1. 分块哈希（防哈希洪水攻击）
byte[] apkContent = readAllBytes(apkFile);
List<byte[]> chunks = split(apkContent, 1MB);
List<Digest> contentDigests = new ArrayList<>();
for (byte[] chunk : chunks) {
    contentDigests.add(new Digest("SHA-256", sha256(chunk)));
}

// 2. 构建签名数据（SignedData）
SignedData signedData = new SignedData();
signedData.setDigests(contentDigests);
signedData.setCertificates(loadCertificates()); // 开发者证书链
signedData.setMinSignatureSchemeId(2); // 最低签名方案
signedData.addOptionalAttribute("target_sdk", 34);

// 3. 使用私钥签名
byte[] signatureBytes = sign(signedData.toByteArray(), privateKey, "SHA256withRSA");

// 4. 构建签名块
ApkSigningBlock block = new ApkSigningBlock();
block.addIdValue(0x7109871a, serialize(signedData, signatureBytes, publicKey));

// 5. 写入 APK（插入在 ZIP 数据后、EOCD 前）
writeSigningBlock(apkOutputStream, block);

android {
    signingConfigs {
        release {
            storeFile file("my-release-key.jks")
            storePassword "your_store_password"
            keyAlias "my-key-alias"
            keyPassword "your_key_password"
            
            // 推荐：同时启用 v1 和 v2
            v1SigningEnabled true
            v2SigningEnabled true
            v3SigningEnabled true  // Android 9+
        }
    }
    
    buildTypes {
        release {
            signingConfig signingConfigs.release
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

# 1. 生成密钥库（首次）
keytool -genkey -v -keystore my-upload-key.jks \
    -keyalg RSA \
    -keysize 2048 \
    -validity 10000 \
    -dname "CN=Your Name, O=Your Org, L=City, ST=State, C=CN" \
    -alias upload-key

# 2. 签名 APK
apksigner sign \
    --key-pass pass:your_key_password \
    --ks-pass pass:your_store_password \
    --ks my-release-key.jks \
    --ks-key-alias my-key-alias \
    --v1-signing-enabled true \
    --v2-signing-enabled true \
    --v3-signing-enabled true \
    app-release-unsigned.apk

# 3. 验证签名
apksigner verify --verbose app-release-unsigned.apk

# 查看 APK 的签名证书
keytool -printcert -jarfile app-release.apk

# 输出示例：
# Owner: CN=Your Name, OU=Your Org, O=Your Company
# Issuer: CN=Your Name, OU=Your Org, O=Your Company
# Serial number: 5f8e2d1c
# Valid from: Tue Oct 14 00:00:00 CST 2025 until: Fri Jan 22 00:00:00 CST 2053
# Certificate fingerprints:
#   SHA1: AA:BB:CC:DD:EE:FF:11:22:33:44:55:66:77:88:99:00:11:22:33:44
#   SHA256: 1A:2B:3C:4D:5E:6F:7A:8B:9C:0D:1E:2F:3A:4B:5C:6D:7E:8F:9A:0B:1C:2D:3E:4F:5A:6B:7C:8D:9E:0F:1A:2B

apksigner verify --verbose --print-certs app-release.apk

# 输出包含：
# Signer #1 certificate SHA-256 digest: ...
# Digest using Digest SHA-256: ...
# Signature algorithm: SHA256withRSA
# Signed using apksigner: true
# Signer #1: 
#   Digest: SHA-256
#   Signature: SHA256withRSA
#   Signed: true