64 lines
2.1 KiB
TypeScript
64 lines
2.1 KiB
TypeScript
import { from_hex } from 'libsodium-wrappers-sumo';
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import { concatUInt8Array, LibSodiumWrappers } from '../crypto';
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export function generateBlindingFactor(serverPk: string, sodium: LibSodiumWrappers) {
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const hexServerPk = from_hex(serverPk);
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const serverPkHash = sodium.crypto_generichash(64, hexServerPk);
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if (!serverPkHash.length) {
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throw new Error('generateBlindingFactor: crypto_generichash failed');
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}
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// Reduce the server public key into an ed25519 scalar (`k`)
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const k = sodium.crypto_core_ed25519_scalar_reduce(serverPkHash);
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return k;
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}
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export function combineKeys(
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lhsKeyBytes: Uint8Array,
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rhsKeyBytes: Uint8Array,
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sodium: LibSodiumWrappers
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) {
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return sodium.crypto_scalarmult_ed25519_noclamp(lhsKeyBytes, rhsKeyBytes);
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}
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// Calculate a shared secret for a message from A to B:
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//
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// BLAKE2b(a kB || kA || kB)
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//
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// The receiver can calculate the same value via:
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//
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// BLAKE2b(b kA || kA || kB)
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export function sharedBlindedEncryptionKey({
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fromBlindedPublicKey,
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otherBlindedPublicKey,
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secretKey,
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sodium,
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toBlindedPublicKey,
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}: {
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secretKey: Uint8Array;
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otherBlindedPublicKey: Uint8Array;
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fromBlindedPublicKey: Uint8Array;
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toBlindedPublicKey: Uint8Array;
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sodium: LibSodiumWrappers;
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}) {
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const aBytes = generatePrivateKeyScalar(secretKey, sodium);
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const combinedKeyBytes = combineKeys(aBytes, otherBlindedPublicKey, sodium);
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return sodium.crypto_generichash(
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32,
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concatUInt8Array(combinedKeyBytes, fromBlindedPublicKey, toBlindedPublicKey)
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);
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}
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// Calculate k*a. To get 'a' (the Ed25519 private key scalar) we call the sodium function to
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// convert to an *x* secret key, which seems wrong--but isn't because converted keys use the
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// same secret scalar secret (and so this is just the most convenient way to get 'a' out of
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// a sodium Ed25519 secret key)
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export function generatePrivateKeyScalar(secretKey: Uint8Array, sodium: LibSodiumWrappers) {
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return sodium.crypto_sign_ed25519_sk_to_curve25519(secretKey);
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}
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export function toX25519(ed25519PublicKey: Uint8Array, sodium: LibSodiumWrappers) {
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return sodium.crypto_sign_ed25519_pk_to_curve25519(ed25519PublicKey);
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}
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