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CAST Encryption
Tool Description
CAST Encryption is an online CAST-128 (CAST5) encryption/decryption tool, supporting ECB / CBC / CFB / OFB cipher modes, PKCS#7 / ISO 9797-1 / ANSI X.923 / ISO 10126 / Zero Padding / No Padding padding schemes, and Base64 / Hex / Latin1 output encodings. All operations run locally in the browser — no data is uploaded to any server.
How to Use
- Enter Key
Enter or click the generate button to create a key (CAST-128 uses a fixed 16-byte / 128-bit key)
- Configure Algorithm
Select a cipher mode (ECB / CBC / CFB / OFB). Non-ECB modes require an IV (8 bytes)
- Set Parameters
Choose a padding scheme and output encoding, then paste or type your text in the input area
- Run Conversion
Click "Encrypt" or "Decrypt" to perform the operation
- Get Result
The result will appear on the right. Use Copy or Download to save it, or Swap to exchange input and output
Use Cases
- OpenPGP Compatibility: CAST5 is a mandatory cipher in OpenPGP (RFC 4880), used for data encryption in PGP/GPG communication
- Legacy System Integration: Some older systems or embedded devices use CAST-128 encryption; use this tool to verify or generate compatible data
- Data Protection: Encrypt sensitive data with CAST-128 before storage or transmission — keys never leave your device
Core Advantages
- Completely Free
The tool gives you free daily uses, so everyday light encrypt/decrypt needs are covered at zero cost — no payment required to experience the full feature set.
- Local Processing
All encryption/decryption runs locally in your browser. Plaintext, keys, and ciphertext are never uploaded to any server, maximizing your data privacy.
- PGP Compatibility
Fully supports CAST-128 (CAST5), enabling encryption/decryption compatible verification with the OpenPGP / GnuPG ecosystem.
- Easy to Use
A clean, intuitive interface with no software to install — open the page and use it instantly, including one-click random key generation and result export.
- Instant Results
Processing happens locally and finishes instantly with no server round-trip. Results display on the right side in real time and can be copied or downloaded with one click.
- Cross-Platform
Runs in any modern browser, so Windows, macOS, Linux, and mobile browsers all work without worrying about system compatibility.
Cipher Modes Explained
Different cipher modes determine how data blocks relate to each other, affecting security and applicable scenarios:
| Mode | Full Name | Requires IV | Description |
|---|---|---|---|
| ECB | Electronic Codebook | No | Each block encrypted independently; identical plaintext produces identical ciphertext — not recommended for long texts |
| CBC | Cipher Block Chaining | Yes | Each block depends on the previous ciphertext; high security, most commonly used mode |
| CFB | Cipher Feedback | Yes | Converts block cipher to stream cipher; suitable for real-time encryption |
| OFB | Output Feedback | Yes | Converts block cipher to stream cipher; errors do not propagate |
Padding Schemes Explained
When plaintext length is not a multiple of the block size (8 bytes), padding is required:
- PKCS#5 / PKCS#7 - Most common; pads with the number of missing bytes (e.g., 3 bytes missing → 0x03 0x03 0x03)
- ISO 9797-1 - First byte is 0x80, remaining bytes are 0x00
- ANSI X.923 - Last byte indicates padding length, remaining bytes are 0x00
- ISO 10126 - Last byte indicates padding length, remaining bytes are random
- Zero Padding - Pads with 0x00 to block size; no padding if plaintext is already block-aligned
- No Padding - No padding; plaintext length must be a multiple of block size (8 bytes)
About CAST-128 Algorithm
CAST-128 (also known as CAST5) is a symmetric-key block cipher designed by Carlisle Adams and Stafford Tavares in 1996, defined in RFC 2144. Key characteristics:
- Block Size - 64 bits (8 bytes)
- Key Length - 40~128 bits (this tool uses full 128-bit / 16-byte keys)
- Rounds - 16-round Feistel network structure
- Design Feature - Uses 8×32-bit large S-boxes, larger than DES's 6×4 S-boxes for enhanced security
FAQ
CAST-128 (also known as CAST5) is a symmetric-key block cipher designed by Carlisle Adams and Stafford Tavares in 1996. It is a mandatory cipher in OpenPGP (RFC 4880) and the default symmetric encryption algorithm in GnuPG 1.x, widely used in PGP encrypted communication.
Both are symmetric block ciphers but differ in design: CAST-128 has a 64-bit block size, 40~128-bit key, and 16-round Feistel structure; AES has a 128-bit block size, 128/192/256-bit key, and 10~14-round SPN structure. AES is the modern encryption standard with wider adoption; CAST-128 is primarily used for OpenPGP and legacy system compatibility.
Yes, decryption must use the exact same key, cipher mode, padding scheme, and output encoding as encryption. Otherwise, decryption will fail or produce garbled output.
CBC mode is generally recommended — it is the most commonly used mode with good security and broad compatibility. ECB mode is not recommended for sensitive data as identical plaintext produces identical ciphertext, risking pattern leakage.
Possible reasons: ① Incorrect key or mismatched length (must be 16 bytes); ② Cipher mode or padding scheme does not match what was used for encryption; ③ Wrong output encoding (if Base64 was used for encryption, select Base64 for decryption too); ④ The input is not valid encrypted data.
No. All encryption/decryption operations run entirely in your browser. Your keys and data never leave your device.
Yes. The tool uses UTF-8 encoding to process text and can correctly encrypt and decrypt Chinese, Japanese, Korean, and any other Unicode characters.
A CAST encryption tool is an online symmetric encryption tool for encrypting and decrypting text with CAST-128 (CAST5). It supports multiple cipher modes and padding schemes, with all operations running locally in the browser — ideal for compatible data handling with the OpenPGP / GnuPG ecosystem.
All processing runs locally in the browser, so it is very fast and most text finishes almost instantly. For very long text, the browser processes it in one pass and generally will not noticeably lag; for extremely large content, splitting it into several runs is recommended.
Yes, mobile is supported. The tool runs in a web page, so mobile browsers (iOS Safari, Android Chrome, etc.) can open and use it directly. The layout is responsive, so you can encrypt and decrypt anytime, anywhere.
This tool uses pure browser-local computation and never uploads data to a server, so its privacy protection is on par with ordinary local software. Compared with third-party software that requires installation and may bundle plugins or collect data, local online computation is lighter and more transparent.
The tool gives you free daily uses, so everyday light encrypt/decrypt needs are covered at zero cost; for higher quotas or more frequent use, a membership unlocks more benefits. Using the basic features requires no registration or login — just open the page and start.
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