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31 lines
658 B
Go
31 lines
658 B
Go
package xsecretbox
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import (
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"errors"
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"github.com/aead/chacha20/chacha"
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"golang.org/x/crypto/curve25519"
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)
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// SharedKey computes a shared secret compatible with the one used by `crypto_box_xchacha20poly1305``
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func SharedKey(secretKey [32]byte, publicKey [32]byte) ([32]byte, error) {
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var sharedKey [32]byte
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sk, err := curve25519.X25519(secretKey[:], publicKey[:])
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if err != nil {
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return sharedKey, err
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}
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c := byte(0)
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for i := 0; i < 32; i++ {
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sharedKey[i] = sk[i]
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c |= sk[i]
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}
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if c == 0 {
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return sharedKey, errors.New("weak public key")
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}
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var nonce [16]byte
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chacha.HChaCha20(&sharedKey, &nonce, &sharedKey)
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return sharedKey, nil
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}
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