/**
 * Cryptographic verification functions
 * Pure functions for signature verification across different algorithms
 *
 * These functions are designed to be:
 * - Pure (no side effects)
 * - Testable in isolation
 * - Reusable across different units
 * - Well-validated with proper error handling
 *
 * @author Synet Team
 */
/**
 * Validate base64 format
 * Ensures the signature is properly formatted base64 before crypto operations
 */
export declare function isValidBase64(str: string): boolean;
/**
 * Validate base64url format
 * Ensures the signature is properly formatted base64url before crypto operations
 */
export declare function isValidBase64Url(str: string): boolean;
/**
 * Normalize signature to base64 format for crypto operations
 * Accepts both base64 and base64url formats
 */
export declare function normalizeSignature(signature: string): string | null;
/**
 * Verify Ed25519 signature
 * @param data The original data that was signed
 * @param signature The signature in base64 or base64url format
 * @param publicKey The public key in PEM format
 * @returns true if signature is valid, false otherwise
 */
export declare function verifyEd25519(data: string, signature: string, publicKey: string): boolean;
/**
 * Verify RSA signature
 * @param data The original data that was signed
 * @param signature The signature in base64 or base64url format
 * @param publicKey The public key in PEM format
 * @returns true if signature is valid, false otherwise
 */
export declare function verifyRSA(data: string, signature: string, publicKey: string): boolean;
/**
 * Verify secp256k1 signature
 * @param data The original data that was signed
 * @param signature The signature in base64 or base64url format
 * @param publicKey The public key in PEM format
 * @returns true if signature is valid, false otherwise
 */
export declare function verifySecp256k1(data: string, signature: string, publicKey: string): boolean;
/**
 * Generic verification function that dispatches to specific algorithms
 * @param data The original data that was signed
 * @param signature The signature in base64 or base64url format
 * @param publicKey The public key in PEM format
 * @param keyType The key type/algorithm
 * @returns true if signature is valid, false otherwise
 */
export declare function verifySignature(data: string, signature: string, publicKey: string, keyType: 'ed25519' | 'rsa' | 'secp256k1' | 'x25519' | 'wireguard'): boolean;