/**
 * Decode a base64url string (unpadded, URL-safe alphabet) to bytes.
 * Returns null on any malformed input rather than throwing, so callers
 * can route the failure to a 'malformed' resolution status.
 *
 * Strictness:
 *  - rejects standard-base64 chars (`+`, `/`) and padding (`=`).
 *  - rejects empty input and whitespace.
 *  - the trailing partial group is validated: stray high bits in the
 *    final sextet (which would make the encoding non-canonical) are
 *    rejected so two distinct strings can never decode to the same key.
 */
export declare function decodeBase64Url(input: string): Uint8Array | null;
/** Lowercase hex of a byte array. */
export declare function bytesToHex(bytes: Uint8Array): string;
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