Encrypt with a=5, b=8
text = HELLOa = 5b = 8mode = encrypt
Result: RCLLA
Affine Cipher Demo
EDUCATIONAL DEMONSTRATION ONLY - The Affine cipher uses a linear mathematical function to map each letter. It combines a multiplicative cipher with an additive cipher. The key a must be coprime with 26.
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Enter your values and press Calculate — the result appears here.
Worked examples
Frequently asked questions
Why must a be coprime with 26?
If a shares a factor with 26, the mapping is not bijective — multiple letters would map to the same output, making decryption impossible.
How many valid keys exist?
There are 12 valid values for a (coprime with 26) × 26 values for b = 312 possible keys. Still trivially breakable by brute force.
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