AES-256-CBC + HMAC-SHA256 Encryption
Classic block cipher encryption with separate message authentication. Encrypt-then-MAC design with PKCS7 padding.
🔐 Your Data is Fully Protected
Your data is fully protected using military-grade AES-256 encryption. We never store your data, passwords, or encrypted results anywhere on our website or in any database.
About This Algorithm
Encryption: AES-256-CBC
- Cipher Block Chaining mode
- 256-bit encryption key
- 16-byte random IV per encryption
- PKCS7 padding (automatic)
Authentication: HMAC-SHA256
- Separate key for authentication
- HMAC covers salt + IV + ciphertext
- Encrypt-then-MAC for security
- Prevents padding oracle attacks
Remember this password - you'll need it to decrypt the data
About AES-256-CBC + HMAC-SHA256 Encryption
AES-256-CBC + HMAC-SHA256 is the classic block cipher encryption with authentication. CBC (Cipher Block Chaining) is one of the oldest and most battle-tested encryption modes, used for decades in SSL/TLS, disk encryption, and countless other applications. Combined with HMAC-SHA256 in an Encrypt-then-MAC construction, it provides robust security with maximum compatibility across platforms and legacy systems.
Technical Specifications
Encryption Algorithm
AES-256-CBC (Cipher Block Chaining) encrypts data in 16-byte blocks. Each plaintext block is XORed with the previous ciphertext block before encryption, creating a chain that prevents pattern leakage.
Authentication (HMAC)
HMAC-SHA256 computes a 256-bit authentication tag over the ciphertext, IV, and salt. This Encrypt-then-MAC approach prevents padding oracle attacks and detects any tampering.
PKCS7 Padding
Since CBC requires data to be a multiple of 16 bytes, PKCS7 padding is applied. Each padding byte contains the number of bytes added (e.g., 5 bytes of value 0x05). This is automatically handled.
Key Derivation
PBKDF2-HMAC-SHA256 with 100,000 iterations. Two separate 256-bit keys are derived: one for AES encryption and one for HMAC, ensuring cryptographic key separation.
How CBC Mode Works
1. Initialization: A random 128-bit Initialization Vector (IV) starts the chain. The IV doesn't need to be secret but must be unique for each encryption with the same key.
2. Block Chaining: Each 16-byte plaintext block is XORed with the previous ciphertext block (or IV for the first block), then encrypted with AES-256. This creates dependencies between blocks.
3. Padding: If the plaintext isn't a multiple of 16 bytes, PKCS7 padding adds bytes until it is. The padding value indicates how many bytes were added.
4. Authentication: After encryption, HMAC-SHA256 is computed over (salt || IV || ciphertext) using a separate MAC key. This tag is verified before decryption.
Why Use CBC+HMAC?
✓ Advantages
- • Maximum compatibility: Works with virtually all systems
- • Battle-tested: Decades of cryptanalysis and real-world use
- • Key separation: Independent encryption and MAC keys
- • Widely understood: Extensive documentation and tooling
- • Proven security: Encrypt-then-MAC is formally verified
⚠ Considerations
- • Requires PKCS7 padding (slightly larger output)
- • Sequential encryption (no parallelization)
- • Must verify HMAC before decrypting (critical!)
- • Two-pass processing (encrypt, then MAC)
- • Padding oracle attacks possible if HMAC not verified first
🔐 Why Encrypt-then-MAC?
This construction verifies the HMAC before attempting decryption. This is critical for CBC mode because it prevents padding oracle attacks—a class of attacks where an attacker can decrypt ciphertext by observing whether decryption succeeds or fails. By verifying the MAC first, we never even attempt to decrypt tampered data.
Comparison with Other Modes
| Feature | AES-GCM | CTR+HMAC | CBC+HMAC |
|---|---|---|---|
| Cipher Type | Stream (CTR-based) | Stream cipher | Block cipher |
| Padding Required | No | No | Yes (PKCS7) |
| Parallelizable | Yes | Yes | Decrypt only |
| Compatibility | Modern systems | Most systems | Universal |
| Best For | Speed, modern protocols | Key separation | Legacy, maximum compatibility |
How Your Data is Protected
This tool uses secure server-side processing with the industry-standard AES-256-CBC encryption algorithm combined with HMAC-SHA256 for message authentication. The implementation follows the Encrypt-then-MAC pattern: encryption is performed first, then HMAC is computed over the complete ciphertext including IV and salt. During decryption, the HMAC is verified before any attempt to decrypt, preventing padding oracle attacks. Your data is fully protected during transmission and processing—we never store your plaintext, password, or encrypted results anywhere on our website or in any database. All data is processed in isolated memory and immediately discarded after your encryption/decryption is complete.