rules:
  - id: auth.java.crypto.ecb-mode
    languages:
      - java
    severity: ERROR
    message: |
      A JCA `Cipher` is being created in ECB mode (or with a bare algorithm
      alias that defaults to ECB). ECB encrypts each block independently, so
      identical plaintext blocks produce identical ciphertext blocks. It is
      deterministic and leaks structure/patterns of the plaintext (CWE-327).
      `Cipher.getInstance("AES")`, `"DES"`, `"DESede"`, or `"Blowfish"` with no
      mode specified silently falls back to ECB as well.

      Use an authenticated mode: `Cipher.getInstance("AES/GCM/NoPadding")` with
      a unique 12-byte IV per message. At minimum use CBC with a random IV plus
      a separate HMAC (encrypt-then-MAC). Never use ECB or a bare cipher alias.
    # Match only the transformation string passed to Cipher.getInstance(...).
    # The metavariable-regex flags either a bare symmetric algorithm alias
    # (AES / DES / DESede / Blowfish with no mode: these default to ECB) or an
    # explicit ECB mode on one of those block ciphers (any padding). It is
    # scoped to symmetric block ciphers on purpose: "AES/GCM/NoPadding" and
    # "AES/CBC/PKCS5Padding" have a safe mode, and "RSA/ECB/OAEPWith..." is
    # asymmetric (the "/ECB/" token there is a JCA quirk, not block-ECB), so
    # none of them match.
    patterns:
      - pattern: javax.crypto.Cipher.getInstance($TRANSFORM, ...)
      - metavariable-regex:
          metavariable: $TRANSFORM
          regex: (?i)^"(aes|des|desede|blowfish)(/ecb/.*)?"$
    metadata:
      oauthlint-rule-id: AUTH-JAVA-CRYPTO-003
      oauthlint-doc-url: https://oauthlint.dev/rules/java-crypto-ecb-mode
      category: security
      cwe: CWE-327
      owasp: A02:2021
      llm-prevalence: MEDIUM
      technology:
        - javax.crypto
      references:
        - https://cwe.mitre.org/data/definitions/327.html
        - https://owasp.org/Top10/A02_2021-Cryptographic_Failures/
        - https://cheatsheetseries.owasp.org/cheatsheets/Cryptographic_Storage_Cheat_Sheet.html