AES Cipher

The AES Cipher (Advanced Encryption Standard) is a widely used symmetric block cipher designed to securely encrypt data. AES operates on 128-bit blocks using keys of 128, 192, or 256 bits and applies a series of substitution-permutation rounds to transform plaintext into ciphertext. It is a standard encryption algorithm in modern cryptography, replacing older systems like DES and 3DES due to its higher security and efficiency.

This AES tool supports multiple operation modes including ECB, CBC, CFB, and OFB. Padding schemes such as PKCS7, ISO10126, ANSI X.923, Zero Padding, and No Padding ensure that plaintext fits the 128-bit block size. The key length can be selected between 128, 192, and 256 bits, affecting the number of rounds AES applies internally. Outputs can be formatted in Base64 or Hexadecimal.

AES Cipher: Encoding Example

With the default configuration:

• Mode: ECB
• Padding: PKCS7
• Key: 0cd44795da015603afe71bc044edee768da26ec8a275f85eb16ecc5e284d3535 (256-bit)
• Format: Base64

Encoding the plaintext hello world produces the following ciphertext:

Plaintext: hello world
Key:       0cd44795da015603afe71bc044edee768da26ec8a275f85eb16ecc5e284d3535
Mode:      ECB
Padding:   PKCS7

Ciphertext (Base64):
zWA6jjOgxulgoiR7gEygDg==

AES encrypts the plaintext in 128-bit blocks, applies the selected padding, and transforms the data into ciphertext using the selected key and mode. The result is encoded as Base64 for convenient display.

AES Cipher: Decoding Example

Using the same key and settings, the ciphertext above can be decrypted back into plaintext:

Ciphertext: zWA6jjOgxulgoiR7gEygDg==
Key:        0cd44795da015603afe71bc044edee768da26ec8a275f85eb16ecc5e284d3535
Mode:       ECB
Padding:    PKCS7

Plaintext:
hello world

Correct decoding requires matching the mode, key, padding, and output format used during encoding. Any mismatch will result in incorrect or failed decryption.

AES Cipher: Usage Notes

• Key Length: AES allows keys of 128, 192, or 256 bits. The key is normalized internally to match the selected length.
• Initialization Vector (IV): Required for modes other than ECB (CBC, CFB, OFB). The IV must match exactly between encryption and decryption.
• Padding: Ensures the plaintext fits the 128-bit block size. Mismatched padding during decryption will cause errors.
• Output Format: Base64 is suitable for transmission and storage; Hex represents the raw bytes.
• Security: AES-256 is recommended for maximum security. ECB mode is not recommended for sensitive data as it does not use an IV and is vulnerable to pattern analysis.

AES remains a cornerstone of modern encryption systems, protecting data in everything from secure communications to file storage, making it essential for understanding symmetric cryptography and block cipher modes.