Add buffer-based PBKDF2 API and validation tests

include/hmac_cpp/hmac_utils.hpp

@@ -70,6 +70,29 @@ namespace hmac_cpp {
                       iterations, dk_len, prf);
     }
 
+    /// \brief Derives PBKDF2-HMAC-SHA256 into caller-provided buffer
+    /// \param password_ptr Pointer to the password buffer
+    /// \param password_len Length of the password in bytes
+    /// \param salt_ptr Pointer to the salt buffer
+    /// \param salt_len Length of the salt in bytes
+    /// \param iterations Number of iterations, must be positive
+    /// \param out_ptr Output buffer for derived key
+    /// \param dk_len Length of output buffer in bytes, must be positive
+    /// \return true on success, false on invalid parameters
+    bool pbkdf2_hmac_sha256(const void* password_ptr, size_t password_len,
+                            const void* salt_ptr, size_t salt_len,
+                            uint32_t iterations, uint8_t* out_ptr, size_t dk_len) noexcept;
+
+    template<size_t N>
+    inline bool pbkdf2_hmac_sha256(const std::string& password,
+                                   const std::string& salt,
+                                   uint32_t iterations,
+                                   std::array<uint8_t, N>& out) noexcept {
+        return pbkdf2_hmac_sha256(password.data(), password.size(),
+                                  salt.data(), salt.size(),
+                                  iterations, out.data(), out.size());
+    }
+
     std::vector<uint8_t> pbkdf2_with_pepper(
             const void* password_ptr, size_t password_len,
             const void* salt_ptr, size_t salt_len,

src/hmac_utils.cpp

@@ -5,6 +5,7 @@
 #include <stdexcept>
 #include <limits>
 #include <algorithm>
+#include <cstring>
 
 namespace hmac_cpp {
 
@@ -107,6 +108,60 @@ namespace hmac_cpp {
         return derived;
     }
 
+    bool pbkdf2_hmac_sha256(const void* password_ptr, size_t password_len,
+                            const void* salt_ptr, size_t salt_len,
+                            uint32_t iterations, uint8_t* out_ptr, size_t dk_len) noexcept {
+        if ((password_len > 0 && password_ptr == nullptr) ||
+            (salt_len > 0 && salt_ptr == nullptr) ||
+            out_ptr == nullptr)
+            return false;
+        if (iterations < 1 || dk_len == 0 || salt_len < 16)
+            return false;
+
+        const size_t hlen = hmac_hash::SHA256::DIGEST_SIZE;
+        uint64_t max_dk = (static_cast<uint64_t>(1) << 32) - 1;
+        max_dk *= hlen;
+        if (dk_len > max_dk)
+            return false;
+
+        size_t l = (dk_len + hlen - 1) / hlen;
+        size_t r = dk_len - (l - 1) * hlen;
+
+        std::vector<uint8_t> salt_block;
+        salt_block.reserve(salt_len + 4);
+        salt_block.insert(salt_block.end(),
+                          reinterpret_cast<const uint8_t*>(salt_ptr),
+                          reinterpret_cast<const uint8_t*>(salt_ptr) + salt_len);
+        salt_block.resize(salt_len + 4);
+
+        size_t pos = 0;
+        for (size_t i = 1; i <= l; ++i) {
+            salt_block[salt_len    ] = static_cast<uint8_t>((i >> 24) & 0xFF);
+            salt_block[salt_len + 1] = static_cast<uint8_t>((i >> 16) & 0xFF);
+            salt_block[salt_len + 2] = static_cast<uint8_t>((i >> 8) & 0xFF);
+            salt_block[salt_len + 3] = static_cast<uint8_t>(i & 0xFF);
+
+            std::vector<uint8_t> u = get_hmac(password_ptr, password_len,
+                                              salt_block.data(), salt_block.size(),
+                                              TypeHash::SHA256);
+            std::vector<uint8_t> t = u;
+            for (uint32_t j = 1; j < iterations; ++j) {
+                u = get_hmac(password_ptr, password_len,
+                              u.data(), u.size(), TypeHash::SHA256);
+                for (size_t k = 0; k < t.size(); ++k) {
+                    t[k] ^= u[k];
+                }
+            }
+            size_t take = (i == l) ? r : hlen;
+            std::memcpy(out_ptr + pos, t.data(), take);
+            pos += take;
+            secure_zero(u.data(), u.size());
+            secure_zero(t.data(), t.size());
+        }
+        secure_zero(salt_block.data(), salt_block.size());
+        return true;
+    }
+
     std::vector<uint8_t> pbkdf2_with_pepper(
             const void* password_ptr, size_t password_len,
             const void* salt_ptr, size_t salt_len,

test_all.cpp

@@ -5,6 +5,8 @@
 #include <limits>
 #include <cerrno>
 #include <random>
+#include <array>
+#include <algorithm>
 #include <openssl/evp.h>
 
 #include "hmac_cpp/hmac.hpp"
@@ -224,6 +226,17 @@ TEST(PBKDF2Validation, ShortSaltThrows) {
     EXPECT_THROW(hmac::pbkdf2("password", "salt", 2, 20, hmac::Pbkdf2Hash::Sha1), std::invalid_argument);
 }
 
+TEST(PBKDF2Validation, ZeroIterationsThrows) {
+    std::string salt(16, 'a');
+    EXPECT_THROW(hmac::pbkdf2("password", salt, 0, 32, hmac::Pbkdf2Hash::Sha256), std::invalid_argument);
+}
+
+TEST(PBKDF2Validation, TooLargeDkLenThrows) {
+    std::string salt(16, 'a');
+    size_t too_large = (static_cast<uint64_t>(1) << 32) * 20;
+    EXPECT_THROW(hmac::pbkdf2("password", salt, 1, too_large, hmac::Pbkdf2Hash::Sha1), std::invalid_argument);
+}
+
 TEST(PBKDF2Test, SHA256WithValidSalt) {
     auto salt = from_hex("000102030405060708090a0b0c0d0e0f");
     std::string salt_str(salt.begin(), salt.end());
@@ -233,6 +246,16 @@ TEST(PBKDF2Test, SHA256WithValidSalt) {
     EXPECT_TRUE(hmac::constant_time_equals(dk, ref));
 }
 
+TEST(PBKDF2BufferApiTest, SHA256ArrayOutput) {
+    auto salt = from_hex("000102030405060708090a0b0c0d0e0f");
+    std::string salt_str(salt.begin(), salt.end());
+    std::array<uint8_t,32> out{};
+    ASSERT_TRUE(hmac::pbkdf2_hmac_sha256(std::string("password"), salt_str, 2, out));
+    std::vector<uint8_t> ref(32);
+    ASSERT_TRUE(PKCS5_PBKDF2_HMAC("password", 8, salt.data(), salt.size(), 2, EVP_sha256(), ref.size(), ref.data()));
+    EXPECT_TRUE(std::equal(out.begin(), out.end(), ref.begin()));
+}
+
 // SHA512 vector from BoringSSL pbkdf_test.cc
 TEST(PBKDF2Test, BoringSSL_SHA512) {
     auto dk = hmac::pbkdf2("passwordPASSWORDpassword",