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Security Updates (April 2026)

This document outlines the security improvements and bug fixes implemented in April 2026 to ensure the library follows modern cryptographic best practices.

1. Hashing Before Signing

Issue: The sign and isSignatureValid methods in MyCrypt (HMAC) and MyKeyPair (RSASSA-PSS) were directly processing the message bytes. While functional, it is a best practice to sign a fixed-length cryptographic hash of the message rather than the variable-length message itself, especially for very large payloads. Fix:

  • Centralized Hashing: Added a Helper.hash(String message) method that computes a SHA-256 digest.
  • Improved Signing: Updated all sign and isSignatureValid implementations in MyCrypt and MyKeyPair to hash the message first using SHA-256. This ensures consistent performance and adheres to stronger cryptographic patterns.
  • Updated Interfaces: Refined the SymmetricCipher and AsymmetricCipher Javadocs and documentation to reflect this architectural change.

Security Updates (March 2026)

This document outlines the security improvements and bug fixes implemented in March 2026 to ensure the library follows modern cryptographic best practices and handles edge cases robustly.

1. Password-Based Key Derivation (PBKDF2) Fix

Issue: The MyCrypt.generateKeyFromPassword method was generating a random salt internally but neither storing nor returning it. This made it impossible for a user to re-derive the same key later (e.g., after an application restart) even with the correct password. Fix:

  • Refactored generateKeyFromPassword(String password) to return the randomly generated byte[] salt.
  • Added an overloaded generateKeyFromPassword(String password, byte[] salt) method to allow users to provide a previously generated salt for consistent key re-derivation.

2. Transition to Modern SecureRandom

Issue: Several classes were explicitly requesting the SHA1PRNG algorithm for SecureRandom. While widely used in the past, SHA1PRNG is now considered legacy, and explicit selection can sometimes lead to platform-specific limitations or weakened entropy if not handled carefully by the provider. Fix: Replaced SecureRandom.getInstance("SHA1PRNG") with new SecureRandom(). This allows the JVM to use the strongest available default provider for the platform (e.g., DRBG on modern OpenJDK), ensuring higher quality entropy.

3. RSA Key Strength Upgrade

Issue: The default RSA key size in MyKeyPair was set to 1024 bits. 1024-bit RSA is no longer considered secure against well-funded attackers and has been deprecated by NIST for several years. Fix: Increased the default RSA key size to 2048 bits, which is the current industry standard for minimum acceptable security.

4. Robust Symmetric Decryption

Issue: MyCrypt.decrypt was susceptible to an ArrayIndexOutOfBoundsException or IllegalArgumentException if provided with malformed or truncated ciphertext (shorter than the 12-byte IV). Fix: Added explicit length validation at the start of the decrypt method. It now throws a clear IllegalArgumentException if the input is too short, preventing low-level runtime crashes.

5. Improved Signature Extraction in Secure Email

Issue: MySecureEmail.decryptAndVerify relied on a simple string split (.split("\n\n---SIGNATURE---\n")) to separate the message body from the digital signature. If the message body happened to contain the delimiter string, extraction would fail or become corrupted. Fix: Updated the logic to use lastIndexOf(delimiter). This ensures that even if the delimiter appears within the message text, the actual signature (which is always appended at the very end) is correctly isolated.

6. Charset Consistency

Issue: MyKeyPair.isSignatureValid was using the platform's default charset when converting the message String to bytes. This could lead to signature verification failures if the code was run on different systems with different default encodings (e.g., UTF-8 vs. Windows-1252). Fix: Explicitly specified StandardCharsets.UTF_8 for all String-to-byte conversions, ensuring consistent behavior across all platforms.

7. Improved Separation of Concerns and Symmetric Signing

Issue: Common cryptographic utilities (like byte array concatenation and hex string conversion) were duplicated across several classes. Additionally, while the library supported asymmetric signatures (RSA), it lacked a standard way to perform symmetric signing (HMAC), which is often more efficient for message authentication. Fix:

  • Centralized Utilities: Moved appendByteArray and bytesToHexString to the Helper class. This reduces code duplication and ensures a single, well-tested implementation for these core binary operations.
  • Symmetric Signing (HMAC-SHA256): Added sign and isSignatureValid methods to the SymmetricCipher interface and implemented them in MyCrypt using HMAC-SHA256. This provides a consistent API for both symmetric and asymmetric message authentication.
  • Refined Encryption: Updated MyCrypt.encrypt to use the centralized Helper.appendByteArray utility for prepending Initialization Vectors (IVs) to ciphertexts, improving code readability and maintainability.