AES Encryption Function
Free online AES encrypt and decrypt tool supporting 128/256 bit encryption online. Includes CBC, ECB, CFB, OFB, and CTR modes, with Hex/Base64 format conversion.
AES Encryption Knowledge
Background of AES Algorithm
The AES algorithm officially replaced DES as the new generation encryption standard in 2001. This transformation originated from a global algorithm solicitation activity initiated by the National Institute of Standards and Technology (NIST). After rigorous screening, the Rijndael algorithm ultimately prevailed and was established as Federal Information Processing Standard FIPS 197, marking the entry of encryption technology into a new stage of development.
Common Application Scenarios
- Government/military communication encryption
- Financial transaction data protection
- Enterprise sensitive document storage
- SSL/TLS network transmission encryption
Operation Modes
Mode Comparison Table
| Mode | Initialization Vector | Parallelism | Error Propagation |
|---|---|---|---|
| CBC | Required | None | Block-level |
| CTR | Counter Initial Value | Supported | No propagation |
Padding Modes
| Mode | Standard Document | Padding Scheme | Use Case |
|---|---|---|---|
| PKCS#7 | RFC 5652 | Pad n bytes with value n | General data |
| ZeroPadding | Industry Practice | Pad with 0x00 bytes | Binary data |
| ISO/IEC 7816-4 | ISO Standard | First byte 0x80 followed by 0x00 | Smart card apps |
Key Length
- Standard Lengths: 128/192/256 bits
- Selection Criteria:
- 128 bits: Regular commercial applications
- 256 bits: Government/military grade data
- Compatibility: Complies with NIST SP 800-131A
Security Considerations
- IV Management Standards:
- CBC mode uses cryptographically secure random numbers
- CTR mode counter never repeats
- Key Derivation:
- Recommended PBKDF2-HMAC-SHA256
- Iteration count ≥10,000 times
- Authenticated Encryption:
- Avoid using ECB mode
References
- [FIPS 197] Advanced Encryption Standard (AES) https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf
- [SP 800-38A] Block Cipher Modes of Operation https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a.pdf
- [RFC 5652] PKCS #7 Cryptographic Message Syntax Specification https://tools.ietf.org/html/rfc5652
- [RFC 5652] https://tools.ietf.org/html/rfc5652
Frequently Asked Questions (FAQ)
What is AES encryption?
Advanced Encryption Standard (AES) is a symmetric encryption algorithm established by the U.S. NIST. It uses the same key for both encryption and decryption and is widely considered the global standard for securing sensitive data.
What is the difference between AES-128, AES-192, and AES-256?
The numbers refer to the length of the encryption key in bits. AES-128 uses a 16-byte key, AES-192 uses a 24-byte key, and AES-256 uses a 32-byte key. AES-256 provides the highest level of security and is often required for military or highly sensitive data.
Which encryption mode (ECB, CBC, CTR, etc.) should I choose?
CBC (Cipher Block Chaining) or CTR (Counter) are the most recommended modes for general use as they provide good security. ECB (Electronic Codebook) is the simplest but least secure mode, as identical plaintext blocks produce identical ciphertext blocks. Avoid ECB unless strictly required.
What is an IV (Initialization Vector) and why do I need it?
An IV is a random or pseudo-random value used in conjunction with the secret key to encrypt data. It ensures that encrypting the same plaintext multiple times produces different ciphertexts. Modes like CBC, CFB, and OFB require an IV (usually 16 bytes for AES).