Differential D7024 Diff 23675 web/media/aes-crypto-utils.js

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web/media/aes-crypto-utils.js

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				// @flow

				const KEY_SIZE = 32; // bytes
				const IV_LENGTH = 12; // bytes - unique Initialization Vector (nonce)
				const TAG_LENGTH = 16; // bytes - GCM auth tag

				async function generateKey(): Promise<Uint8Array> {
				const algorithm = { name: 'AES-GCM', length: 256 };
				const key = await crypto.subtle.generateKey(algorithm, true, [
				'encrypt',
				'decrypt',
				]);
				const keyData = await crypto.subtle.exportKey('raw', key);
				return new Uint8Array(keyData);
				}

				async function encrypt(
				keyBytes: Uint8Array,
				plaintext: Uint8Array,
				): Promise<Uint8Array> {
				if (keyBytes.length !== KEY_SIZE) {
				throw new Error('Invalid AES key size');
				}

				// we're creating the buffer now so we can avoid reallocating it later
				const outputBuffer = new ArrayBuffer(
				plaintext.length + IV_LENGTH + TAG_LENGTH,
				);
				const ivBytes = new Uint8Array(outputBuffer, 0, IV_LENGTH);
				const iv = crypto.getRandomValues(ivBytes);

				const algorithm = { name: 'AES-GCM', iv: iv, tagLength: TAG_LENGTH * 8 };
				const key = await crypto.subtle.importKey('raw', keyBytes, 'AES-GCM', false, [
				'encrypt',
				]);
				const ciphertextWithTag = await crypto.subtle.encrypt(
				algorithm,
				key,
				plaintext,
				);

				const result = new Uint8Array(outputBuffer);
				result.set(new Uint8Array(ciphertextWithTag), iv.length);
				return result;
				}

				async function decrypt(
				keyBytes: Uint8Array,
				sealedData: Uint8Array,
				): Promise<Uint8Array> {
				if (keyBytes.length !== KEY_SIZE) {
				throw new Error('Invalid AES key size');
				}
				if (sealedData.length < IV_LENGTH + TAG_LENGTH) {
				throw new Error('Invalid ciphertext size');
				}

				const iv = sealedData.subarray(0, IV_LENGTH);
				const ciphertextWithTag = sealedData.subarray(IV_LENGTH);

				const algorithm = { name: 'AES-GCM', iv, tagLength: TAG_LENGTH * 8 };
				const key = await crypto.subtle.importKey('raw', keyBytes, 'AES-GCM', false, [
				'decrypt',
				]);

				const plaintextBuffer = await crypto.subtle.decrypt(
				algorithm,
				key,
				ciphertextWithTag,
				);
				return new Uint8Array(plaintextBuffer);
				}

				export { generateKey, encrypt, decrypt };