/**
 * Buffer Utility Functions
 *
 * This module provides utilities for converting between ArrayBuffer and Base64 string formats.
 * These are essential for WebAuthn operations where binary data needs to be serialized for
 * transmission or storage.
 *
 * @module utils/buffer
 */
/**
 * Converts an ArrayBuffer to a Base64-encoded string.
 *
 * This function is commonly used to serialize binary data from WebAuthn credentials
 * (such as credential IDs, attestation objects, and signatures) into a string format
 * suitable for JSON serialization and HTTP transmission.
 *
 * @param buffer - The ArrayBuffer to convert
 * @returns A Base64-encoded string representation of the buffer
 *
 * @example
 * ```typescript
 * const buffer = new Uint8Array([72, 101, 108, 108, 111]).buffer;
 * const base64 = bufferToBase64(buffer);
 * console.log(base64); // "SGVsbG8="
 * ```
 *
 * @remarks
 * This implementation uses a manual conversion approach rather than directly using btoa()
 * on the buffer to ensure compatibility with all buffer sizes and avoid potential issues
 * with binary data containing null bytes.
 */
export declare function bufferToBase64(buffer: ArrayBuffer): string;
/**
 * Converts a Base64 or Base64URL string back to an ArrayBuffer.
 *
 * This function is commonly used to deserialize Base64-encoded credential data
 * received from a server or retrieved from storage back into the binary format
 * required by the WebAuthn API.
 *
 * **Both alphabets are accepted, deliberately.** WebAuthn hands out the same credential in two
 * encodings at once: `bufferToBase64(rawId)` gives standard Base64 (`+`, `/`, padded) while
 * `PublicKeyCredential.id` is Base64URL (`-`, `_`, unpadded). A single result object therefore
 * carries both spellings of one credential:
 *
 * ```
 * credentialId: "bsA9+najCxZLvNhXIg/RawfFH77..."   // standard
 * rawCredential.id: "bsA9-najCxZLvNhXIg_RawfFH77..." // Base64URL
 * ```
 *
 * `atob` rejects `-` and `_` outright, so feeding it the second form threw
 * `InvalidCharacterError: The string to be decoded is not correctly encoded` — an error naming
 * neither the value nor the caller, typically surfacing from an `allowCredentials` entry that had
 * travelled through a store or a JSON round trip that normalised it. Since both spellings denote
 * the same bytes, normalising here is strictly better than making every caller guess which
 * alphabet it holds.
 *
 * Padding is restored too: Base64URL conventionally drops `=`, and `atob` requires it.
 *
 * @param base64 - The Base64 or Base64URL string to convert
 * @returns An ArrayBuffer containing the decoded binary data
 * @throws {Error} If the input is not valid in either alphabet — with the offending value in the
 *   message, unlike the bare DOMException `atob` raises
 *
 * @example
 * ```typescript
 * base64ToBuffer('SGVsbG8=');   // standard, padded
 * base64ToBuffer('SGVsbG8');    // unpadded
 * base64ToBuffer('a-b_c');      // Base64URL
 * ```
 *
 * @remarks
 * The returned ArrayBuffer can be directly used with WebAuthn APIs that expect
 * BufferSource types, such as the `id` field in credential descriptors or the
 * `challenge` field in credential request options.
 */
export declare function base64ToBuffer(base64: string): ArrayBuffer;
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