MuntashirAkon/AppManager · error · IOException

Unsupported encryption method: " + encryptionName

Error message

Unsupported encryption method: " + encryptionName

What it means

IOException from AndroidBackupHeader.decodeAesHeaderAndInitialize: the encryption algorithm name in the backup header does not match the supported AES-256/CBC algorithm name (ENCRYPTION_ALGORITHM_NAME), so decryption cannot proceed.

Solutions

1. Re-create the backup using standard adb backup (AES-256 encryption) or no encryption
2. Compare the header's encryption line against the expected algorithm name to identify the producer
3. Use the original tool that encrypted the backup to decrypt it first, then feed plaintext to the extractor
4. Check for header line misalignment caused by earlier corruption

Example fix

// before
// header line: AES-128-CBC-1.2 (from a non-standard tool) -> throws
InputStream tar = header.toTar();
// after (decrypt externally with the original tool first)
InputStream plain = thirdPartyToolDecrypt(abFile, password);
InputStream tar = new AndroidBackupHeader(plain, null).toTar();

String encLine = readHeaderLine(abFile, 3); // encryption algorithm line
if (!"AES-256-CBC-1.2".equals(encLine) && !"none".equals(encLine)) {
    throw new IOException("Unsupported backup encryption: " + encLine);
}

try {
    InputStream tar = header.toTar();
} catch (IOException e) {
    if (e.getMessage().startsWith("Unsupported encryption method")) {
        Log.e(TAG, "Backup encrypted with a non-standard algorithm; decrypt with the original tool", e);
    } else throw e;
}

When it happens

Trigger: The header's encryption line (line 4) contains a value other than the supported constant — typically "none" mismarked, or a cipher name from a different backup tool; occurs when the header says encrypted but with an unrecognized algorithm.

Common situations: Backups produced by modified adb implementations or third-party tools with custom encryption; corrupted header line shifting values; spoofed/hand-edited headers.

Related errors

• Archive is encrypted but no password given
• Checksums for master key did not match.
• Couldn't delete old file
• Couldn't get misc.am.tsv for generating checksum
• Failed to decrypt

AI-assisted analysis of MuntashirAkon/AppManager@0152f468fc (2026-09-12). Data as JSON: /api/errors/9a1ac056c1e5053e. Report an issue: GitHub.

Appendix: source

Thrown at app/src/main/java/io/github/muntashirakon/AppManager/backup/adb/AndroidBackupHeader.java:237

        mkOut.writeByte(mk.length);
        mkOut.write(mk);
        mkOut.writeByte(checksum.length);
        mkOut.write(checksum);
        mkOut.flush();
        byte[] encryptedMk = mkC.doFinal(blob.toByteArray());
        headerbuf.append(byteArrayToHex(encryptedMk));
        headerbuf.append('\n');

        return finalOutput;
    }

    @NonNull
    private static InputStream decodeAesHeaderAndInitialize(char[] decryptPassword,
                                                            @NonNull String encryptionName,
                                                            boolean pbkdf2Fallback,
                                                            @NonNull InputStream rawInStream) throws Exception {
        if (!encryptionName.equals(ENCRYPTION_ALGORITHM_NAME)) {
            throw new IOException("Unsupported encryption method: " + encryptionName);
        }

        String userSaltHex = readHeaderLine(rawInStream); // 5
        byte[] userSalt = hexToByteArray(userSaltHex);

        String ckSaltHex = readHeaderLine(rawInStream); // 6
        byte[] ckSalt = hexToByteArray(ckSaltHex);

        int rounds = Integer.parseInt(readHeaderLine(rawInStream)); // 7
        String userIvHex = readHeaderLine(rawInStream); // 8

        String encryptionKeyBlobHex = readHeaderLine(rawInStream); // 9

        // decrypt the encryption key blob
        try {
            return attemptEncryptionKeyDecryption(decryptPassword, PBKDF_CURRENT, userSalt,
                    ckSalt, rounds, userIvHex, encryptionKeyBlobHex, rawInStream);
        } catch (Exception e) {

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