Cryptography & Security

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Collision Probability

Approximate chance of a collision among n items in space N.

Formula

P \approx \frac{n^2}{2N}

Variables

PCollision probability

nNumber of items

NSize of space

Example

n=1000, N=10^9: P ≈ 5×10⁻⁴

Did You Know?

UUID and nonce designers use this bound to pick sizes large enough that duplicates essentially never happen.

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