https://github.com/aldantanneo/bigints

WIP constant time bigint implementation in SPARK
https://github.com/aldantanneo/bigints

ada bigint cryptography formal-verification spark

Last synced: 12 days ago
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WIP constant time bigint implementation in SPARK

• Host: GitHub
• URL: https://github.com/aldantanneo/bigints
• Owner: AldanTanneo
• License: mit
• Created: 2024-11-25T13:42:02.000Z (3 months ago)
• Default Branch: main
• Last Pushed: 2025-01-24T14:43:36.000Z (18 days ago)
• Last Synced: 2025-01-24T15:30:56.840Z (18 days ago)
• Topics: ada, bigint, cryptography, formal-verification, spark
• Language: Ada
• Homepage:
• Size: 160 KB
• Stars: 1
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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# SPARK Constant Time Big Integer library

Implementation of a constant time big integer library, heavily inspired by [crypto-bigint](https://github.com/RustCrypto/crypto-bigint).

## Usage

The implementations are generic over the size of the integer

```ada

package U256 is new Bigints.Uint (256);

package U1024 is new Bigints.Uint (1024);

```

There is also a generic package to deal with modular integers (ie, over a prime field)

```ada

P : U256 := ...--  a big prime, like 2^255 - 19

package GF_P is new Bigints.Modular (U256, P);

```

All functions are implemented in constant time, except those with an explicit `_Vartime` suffix. Overloaded operators are also constant time.

> ⚠️ The constant time choice primitives like `Choice_From_Condition`, `Cond_Select`, `CSwap` rely on best-effort optimisation barriers.

## Tests

The library is formally checked using `gnatprove`. When contracts are respected, there cannot be any runtime errors.

Some functional contracts try to go a bit further and prove more advanced behaviours (WIP).

Tests are implemented in `./tests/src/`. Run them (UNIX only) with

```sh

cd tests

./run.sh

```