Insecure Data Exposure Due to AES-ECB Mode Usage

#harmonyos #aesencryption #cryptography #ecbmode

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Problem Description

During development implementation of data encryption using the Crypto Kit. The application stores sensitive user profile information in local storage. During a security review, it was discovered that the encryption was performed with AES in ECB (Electronic Code Book) mode.

Background Knowledge

AES is a symmetric block cipher, but when used in ECB mode it encrypts identical plaintext blocks into identical ciphertext blocks. This pattern leaks structural information about the data, making it vulnerable to cryptanalysis and pattern analysis attacks. HarmonyOS

Crypto Kit provides support for more secure modes such as AES-GCM and AES-CBC, but developers must explicitly configure them.

Troubleshooting Process

1.Reviewed the encryption implementation in the source code.

2.Found the algorithm configuration:

   const params = { algName: "AES", mode: "ECB", // explicitly chosen key: symKey };

3.Confirmed that ciphertext files still contained visible repeating patterns when encrypting repetitive test data (e.g., all-zero blocks).

4.Checked Crypto Kit documentation and verified that AES-ECB is not recommended for sensitive data.

Analysis Conclusion

The fault was not a runtime bug but a misuse of the Crypto Kit API. The insecure AES-ECB mode caused predictable ciphertext patterns, weakening confidentiality guarantees.

Solution

Replace AES-ECB with AES-GCM (preferred for both encryption and authentication) or AES-CBC with randomized IV if AES-GCM is unavailable.
Example correction:

  const iv = new Uint8Array(12); 
  cryptoFramework.generateRandom(iv); 
  const params = { algName: "AES", mode: "GCM", // secure mode iv, key: symKey }; 
  const encrypted = await cryptoFramework.encrypt(params, plainBuffer);

Verification Result

After switching to AES-GCM, repeated plaintext blocks no longer produce repeated ciphertext blocks.
Additional integrity verification was achieved thanks to GCM’s authentication tag.