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IDEA Encryption
About This Tool
IDEA Encryption is an online IDEA (International Data Encryption Algorithm) encryption/decryption tool. IDEA is a symmetric block cipher designed by Xuejia Lai and James L. Massey at ETH Zürich in 1991. It features a 64-bit block size (8 bytes) and a fixed 128-bit key length (16 bytes). This tool supports ECB / CBC / CFB / OFB / CTR cipher modes, PKCS#7 / ISO 9797-1 / ANSI X.923 / ISO 10126 / Zero Padding / No Padding padding schemes, and Base64 / Hex / Latin1 / UTF-8 output encodings. All operations run locally in your browser — no data is ever uploaded to any server.
How to Use
- Generate Key
Enter or click the random button to generate a 16-byte key (IDEA uses a fixed 128-bit key)
- Choose Cipher Mode
Select a cipher mode (ECB / CBC / CFB / OFB / CTR). Non-ECB modes require an IV (8 bytes)
- Pick Padding & Encoding
Choose a padding scheme and output encoding (Base64 / Hex / Latin1 / UTF-8)
- Enter Text
Paste or type the text you want to encrypt/decrypt in the left textarea
- Run & Export
Click "Encrypt" or "Decrypt" to execute. The result will appear on the right side, ready to copy or download
Use Cases
- PGP Compatibility: IDEA was the default symmetric encryption algorithm in PGP (Pretty Good Privacy) email encryption software. Use this tool to work with legacy PGP-encrypted data
- Cryptography Education: IDEA is renowned for its innovative Lai-Massey structure and mixed algebraic operations, making it a classic case study in cryptography textbooks
- Cross-Platform Data Transfer: Encrypt sensitive data with IDEA before transmitting it between different systems or applications to ensure confidentiality during transit
Key Advantages
- Completely Free
The tool gives you free daily uses, so everyday IDEA encryption/decryption needs are covered at zero cost — no membership required for core features
- Local Processing
All encryption runs locally in your browser; your keys and plaintext never leave your device, protecting your privacy to the maximum
- Classic Algorithm
IDEA classic symmetric block cipher built in, compatible with legacy PGP data, with all cipher modes and padding schemes supported
- Easy to Use
Visual parameter configuration with one-click random key generation; no software install needed — just open the page
- Instant Results
Encryption/decryption returns results in real time, supporting Base64, Hex, Latin1 and UTF-8 output encodings with one-click copy or download
- Cross-Platform
Runs in any browser — Windows, macOS, Linux or mobile — so you can perform IDEA encryption/decryption anytime, anywhere
IDEA Algorithm Principles
IDEA (International Data Encryption Algorithm) is a symmetric block cipher designed by Xuejia Lai and James L. Massey in 1991, originally called IPES (Improved Proposed Encryption Standard). It encrypts 64-bit data blocks using a 128-bit key, performing a total of 8.5 rounds of transformation (8 full rounds + 1 output transformation half-round).
IDEA's core innovation lies in its mixed operation design — each round uses three different algebraic group operations: multiplication modulo 2¹⁶+1, addition modulo 2¹⁶, and bitwise XOR. These three operations are algebraically incompatible, greatly enhancing resistance to differential and linear cryptanalysis. As a result, IDEA remained unbroken for nearly 20 years after its introduction.
Security Status: IDEA's patent expired in 2012, and it is now in the public domain. While the 128-bit key is sufficient to resist brute-force attacks, its 64-bit block size poses a theoretical birthday attack risk when encrypting large volumes of data. For new projects, AES-256 is recommended. IDEA is primarily used for legacy data compatibility and cryptography education.
IDEA vs. Other Encryption Algorithms
A comparison of IDEA with DES and AES symmetric encryption algorithms:
| Feature | IDEA | DES | AES |
|---|---|---|---|
| Algorithm Type | Block Cipher | Block Cipher | Block Cipher |
| Key Length | 128 bits (16 bytes) | 56 bits (8 bytes) | 128/192/256 bits |
| Block Size | 64 bits | 64 bits | 128 bits |
| Security | High (128-bit key) | Deprecated (56-bit is brute-forceable) | High, current standard |
Cipher Modes Explained
IDEA supports the following five cipher modes, each with different security properties and use cases:
| Mode | Full Name | IV Required | Description |
|---|---|---|---|
| ECB | Electronic Codebook | No | Each block is encrypted independently. Identical plaintext produces identical ciphertext. Not recommended for multi-block data |
| CBC | Cipher Block Chaining | Yes | Each block is XORed with the previous ciphertext block before encryption. Highly secure and widely used |
| CFB | Cipher Feedback | Yes | Converts the block cipher into a stream cipher. Suitable for real-time encryption |
| OFB | Output Feedback | Yes | Generates a keystream XORed with the plaintext. Transmission errors do not propagate |
| CTR | Counter | Yes | Counter mode, supports parallel processing with excellent performance |
Padding Schemes Explained
When the plaintext length is not a multiple of the block size (8 bytes), padding is required. Here is an explanation of each scheme:
- PKCS#5 / PKCS#7 - The most commonly used padding. If N bytes are missing, fill with N bytes each of value N
- ISO 9797-1 - Starts with 0x80, pads the rest with 0x00 to the block boundary
- ANSI X.923 - Random padding at the end; the last byte records the padding length
- ISO 10126 - Similar to ANSI X.923 but uses random values for padding
- Zero Padding - Fills the end with 0x00 bytes. May conflict with original data ending in null characters
- No Padding - No padding is applied. The plaintext length must be an exact multiple of 8 bytes
FAQ
IDEA uses a 128-bit key, making brute-force attacks computationally infeasible. The algorithm employs the Lai-Massey structure and mixes three different algebraic operations, providing strong resistance to cryptanalysis. It has remained unbroken since its introduction in 1991. However, due to its 64-bit block size, there is a theoretical birthday attack risk when encrypting massive amounts of data. For high-security needs, AES-256 is recommended.
Key differences: ① Block size — IDEA is 64-bit, AES is 128-bit; ② Key length — IDEA is fixed at 128-bit, AES supports 128/192/256-bit; ③ Design structure — IDEA uses the Lai-Massey structure, AES uses the SPN (Substitution-Permutation Network) structure; ④ Standardization — AES is the NIST-selected global encryption standard, while IDEA was the historical default in PGP. Currently, AES is the recommended modern encryption scheme.
IDEA requires the key to be exactly 16 bytes (128 bits). English letters, digits, and symbols each occupy 1 byte, while a single Chinese character occupies 3 bytes. If you entered 16 English letters but validation fails, check for extra whitespace. We recommend clicking the "Generate Random Key" button next to the key input field to automatically create a valid key.
Yes. When decrypting, you must use the exact same key, cipher mode, padding scheme, and output encoding that were used for encryption; otherwise, decryption will fail or produce garbage output. The IV must also match exactly (except in ECB mode). We recommend saving all encryption parameters alongside the ciphertext.
No. All encryption/decryption operations run entirely in your browser. Your keys and plaintext 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. The encrypted output is in Base64, Hex, Latin1, or UTF-8 encoding for safe transmission and storage.
CBC mode is recommended. In ECB mode, identical plaintext blocks produce identical ciphertext blocks, which may leak data patterns (e.g., encrypted images may still reveal outlines). CBC mode introduces an IV to make each encryption result unique, providing significantly higher security. Only consider ECB if you need simple, fast encryption and accept the associated security risks.
IDEA's 128-bit key still resists brute force, but its 64-bit block size carries a theoretical birthday-attack risk at large volumes. For new projects AES is preferred; IDEA's value lies mainly in legacy PGP compatibility and cryptography study. We keep it so you can handle old data easily.
This tool targets real-time text encryption/decryption, ideal for short text such as keys and tokens. For files, watch a future version; the free daily quota covers everyday light use.
Both have similar key lengths (IDEA 128-bit, 3DES effectively 168-bit), but IDEA's more modern design resists analysis better; 3DES also suffers the 64-bit block birthday risk. For new projects neither is recommended over AES.
Never stored. All encryption runs locally in your browser; the key lives only briefly in the page's memory. The tool keeps no keys or plaintext on any server — please save yours yourself.
Yes. The tool runs in any browser, including iOS, Android and desktop, and the page is adapted for mobile so you can use it anywhere.
Content last updated：2026-07-15
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