v4.0.0

Highlights

This is a major release focused on security hardening, a modernised CMake build system, and a new ergonomic context API.

Breaking Changes

• SHA1, SHA256, SHA512 renamed to COTP_SHA1, COTP_SHA256, COTP_SHA512 (thanks to @CppPhil)
• MIN_DIGTS typo fixed to MIN_DIGITS
• typedef unsigned char uchar removed; base32_encode now takes const uint8_t *, base32_decode returns uint8_t *
• b32_alphabet is no longer exported (now static)
• MSVC support dropped
• get_hotp / get_totp / get_totp_at return NULL on all error paths; callers must check the return value and the cotp_error_t output parameter
• The library no longer prints to stderr on errors; all diagnostics are reported via cotp_error_t

New Features

• Context API (cotp_ctx): ergonomic wrapper for repeated TOTP calls with the same configuration (cotp_ctx_create, cotp_ctx_totp, cotp_ctx_totp_at, cotp_ctx_free)
• Optional validation helper (-DCOTP_ENABLE_VALIDATION=ON): validate_totp_in_window() for window-based TOTP verification with timing-safe comparison
• CMake package config: consumers can now use find_package(COTP CONFIG) and link via COTP::cotp

Improvements

• otp_to_int() now validates input for NULL and non-digit characters before conversion
• Base32 get_char_index and valid_b32_str use O(1) lookup tables instead of O(n) loops
• Base32 decode buffer calculation uses exact integer arithmetic instead of floating-point approximation
• islower()/toupper() calls cast to unsigned char to avoid undefined behaviour on signed char

Security Fixes

• Added runtime bounds checks in RFC 4226 truncation and Steam code paths (offset and length validated before array access)
• Fixed potential NULL dereference in OpenSSL backend (whmac_setkey error path now frees context and sets ctx = NULL)
• Fixed OOB read in strip_char (Base32): lookup table was 128 bytes but indexed with full uint8_t range (0–255)
• Fixed undefined behaviour in base32_encode: strlen() on potentially non-NUL-terminated binary input replaced with bounds-safe check
• Added NULL guards to whmac_freehandle() across all three backends
• Fixed MbedTLS whmac_finalize returning buflen instead of actual digest length
• mbedtls_md_hmac_starts() return value is now checked
• Timing-safe comparison (cotp_timing_safe_memcmp) used in TOTP window validation
• cotp_secure_memzero() applied to decoded secrets and HMAC digests immediately after use

Build System

• Added CMake package config (find_package(COTP CONFIG)) alongside existing pkg-config support
• Compiler flags scoped to cotp target only (no longer pollute global scope via add_compile_options)

sha256: 6b17323779dac1699462d8914b81155d69914b0d28b5ed837f1570ed05f2bd90