89 lines
3.5 KiB
TypeScript
89 lines
3.5 KiB
TypeScript
/**
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* HKDF (RFC 5869): extract + expand in one step.
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* See https://soatok.blog/2021/11/17/understanding-hkdf/.
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* @module
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*/
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import { hmac } from './hmac.ts';
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import { ahash, anumber, type CHash, clean, type Input, toBytes } from './utils.ts';
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/**
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* HKDF-extract from spec. Less important part. `HKDF-Extract(IKM, salt) -> PRK`
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* Arguments position differs from spec (IKM is first one, since it is not optional)
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* @param hash - hash function that would be used (e.g. sha256)
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* @param ikm - input keying material, the initial key
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* @param salt - optional salt value (a non-secret random value)
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*/
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export function extract(hash: CHash, ikm: Input, salt?: Input): Uint8Array {
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ahash(hash);
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// NOTE: some libraries treat zero-length array as 'not provided';
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// we don't, since we have undefined as 'not provided'
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// https://github.com/RustCrypto/KDFs/issues/15
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if (salt === undefined) salt = new Uint8Array(hash.outputLen);
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return hmac(hash, toBytes(salt), toBytes(ikm));
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}
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const HKDF_COUNTER = /* @__PURE__ */ Uint8Array.from([0]);
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const EMPTY_BUFFER = /* @__PURE__ */ Uint8Array.of();
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/**
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* HKDF-expand from the spec. The most important part. `HKDF-Expand(PRK, info, L) -> OKM`
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* @param hash - hash function that would be used (e.g. sha256)
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* @param prk - a pseudorandom key of at least HashLen octets (usually, the output from the extract step)
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* @param info - optional context and application specific information (can be a zero-length string)
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* @param length - length of output keying material in bytes
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*/
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export function expand(hash: CHash, prk: Input, info?: Input, length: number = 32): Uint8Array {
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ahash(hash);
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anumber(length);
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const olen = hash.outputLen;
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if (length > 255 * olen) throw new Error('Length should be <= 255*HashLen');
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const blocks = Math.ceil(length / olen);
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if (info === undefined) info = EMPTY_BUFFER;
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// first L(ength) octets of T
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const okm = new Uint8Array(blocks * olen);
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// Re-use HMAC instance between blocks
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const HMAC = hmac.create(hash, prk);
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const HMACTmp = HMAC._cloneInto();
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const T = new Uint8Array(HMAC.outputLen);
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for (let counter = 0; counter < blocks; counter++) {
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HKDF_COUNTER[0] = counter + 1;
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// T(0) = empty string (zero length)
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// T(N) = HMAC-Hash(PRK, T(N-1) | info | N)
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HMACTmp.update(counter === 0 ? EMPTY_BUFFER : T)
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.update(info)
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.update(HKDF_COUNTER)
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.digestInto(T);
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okm.set(T, olen * counter);
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HMAC._cloneInto(HMACTmp);
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}
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HMAC.destroy();
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HMACTmp.destroy();
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clean(T, HKDF_COUNTER);
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return okm.slice(0, length);
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}
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/**
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* HKDF (RFC 5869): derive keys from an initial input.
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* Combines hkdf_extract + hkdf_expand in one step
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* @param hash - hash function that would be used (e.g. sha256)
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* @param ikm - input keying material, the initial key
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* @param salt - optional salt value (a non-secret random value)
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* @param info - optional context and application specific information (can be a zero-length string)
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* @param length - length of output keying material in bytes
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* @example
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* import { hkdf } from '@noble/hashes/hkdf';
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* import { sha256 } from '@noble/hashes/sha2';
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* import { randomBytes } from '@noble/hashes/utils';
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* const inputKey = randomBytes(32);
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* const salt = randomBytes(32);
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* const info = 'application-key';
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* const hk1 = hkdf(sha256, inputKey, salt, info, 32);
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*/
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export const hkdf = (
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hash: CHash,
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ikm: Input,
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salt: Input | undefined,
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info: Input | undefined,
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length: number
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): Uint8Array => expand(hash, extract(hash, ikm, salt), info, length);
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