Merge pull request #69 from faasm/feature-cpabe-hybrid

[accless] Implement CP-ABE Hybrid Scheme

Author: csegarragonz

.github/workflows/azure.yml

@@ -46,6 +46,7 @@ env_logger = "0.11.8"
 futures = "^0.3"
 futures-util = "0.3"
 hex = "0.4.3"
+hkdf = "0.12.4"
 hyper = { version = "1.6.0" }
 hyper-util = { version = "0.1" }
 indicatif = "^0.17"
@@ -81,3 +82,4 @@ uuid = { version = "^1.3" }
 walkdir = "2"
 warp = "^0.3"
 x509-parser = { version = "0.16.0" }
+zeroize = "1.8.2"

Cargo.lock

@@ -14,15 +14,18 @@ crate-type=["rlib", "staticlib"]
 path = "src/lib.rs"
 
 [dependencies]
+aes-gcm = { workspace = true, features = ["aes"] }
 anyhow.workspace = true
 ark-bls12-381.workspace = true
 ark-ec.workspace = true
 ark-ff.workspace = true
 ark-std = { workspace = true, features = ["std"] }
 ark-serialize = { workspace = true, features = ["derive"] }
 base64.workspace = true
+hkdf.workspace = true
 log.workspace = true
 rand = { workspace = true, features = ["std", "std_rng"] }
 serde = { workspace = true, features = ["derive"] }
 serde_json.workspace = true
 sha2.workspace = true
+zeroize.workspace = true

Cargo.toml

@@ -127,6 +127,55 @@ std::optional<std::string> decrypt(const std::string &usk,
     return gt_b64;
 }
 
+namespace hybrid {
+
+EncryptOutput encrypt(const std::string &mpk, const std::string &policy,
+                      const std::vector<uint8_t> &plaintext,
+                      const std::vector<uint8_t> &aad) {
+    std::string plaintext_b64 = accless::base64::encode(plaintext);
+    std::string aad_b64 = accless::base64::encode(aad);
+
+    char *result = encrypt_hybrid_abe4(mpk.c_str(), policy.c_str(),
+                                       plaintext_b64.c_str(), aad_b64.c_str());
+    if (!result) {
+        std::cerr
+            << "accless(abe4): FFI call to encrypt_hybrid_abe4 failed. See "
+               "Rust logs for details."
+            << std::endl;
+        throw std::runtime_error(
+            "accless(abe4): encrypt_hybrid_abe4 FFI call failed");
+    }
+
+    auto result_json = nlohmann::json::parse(result);
+    free_string(result);
+
+    return {result_json["abe_ct"], result_json["sym_ct"]};
+}
+
+std::optional<std::vector<uint8_t>>
+decrypt(const std::string &usk, const std::string &gid,
+        const std::string &policy, const std::string &abe_ct,
+        const std::string &sym_ct, const std::vector<uint8_t> &aad) {
+    std::string aad_b64 = accless::base64::encode(aad);
+    char *result =
+        decrypt_hybrid_abe4(usk.c_str(), gid.c_str(), policy.c_str(),
+                            abe_ct.c_str(), sym_ct.c_str(), aad_b64.c_str());
+    if (!result) {
+        std::cerr
+            << "accless(abe4): FFI call to decrypt_hybrid_abe4 failed. See "
+               "Rust logs for details."
+            << std::endl;
+        return std::nullopt;
+    }
+
+    std::string plaintext_b64(result);
+    free_string(result);
+
+    return accless::base64::decode(plaintext_b64);
+}
+
+} // namespace hybrid
+
 std::map<std::string, std::vector<uint8_t>>
 unpackFullKey(const std::vector<uint8_t> &full_key_bytes) {
     std::map<std::string, std::vector<uint8_t>> result;

accless/libs/abe4/Cargo.toml

@@ -19,6 +19,11 @@ char *keygen_partial_abe4(const char *gid_cstr,
                           const char *partial_msk_b64_cstr,
                           const char *user_attrs_json);
 char *policy_authorities_abe4(const char *policy_str);
+char *encrypt_hybrid_abe4(const char *mpk_b64, const char *policy_str,
+                          const char *plaintext_b64, const char *aad_b64);
+char *decrypt_hybrid_abe4(const char *usk_b64, const char *gid,
+                          const char *policy_str, const char *abe_ct_b64,
+                          const char *sym_ct_b64, const char *aad_b64);
 
 } // extern "C"
 
@@ -208,4 +213,48 @@ std::string packFullKey(const std::vector<std::string> &authorities,
  * @return A vector with all the attributes that appear in the policy.
  */
 std::vector<std::string> getPolicyAuthorities(const std::string &policy);
+
+namespace hybrid {
+struct EncryptOutput {
+    std::string abe_ciphertext;
+    std::string sym_ciphertext;
+};
+
+/**
+ * @brief Encrypts plaintext and associated data using the hybrid CP-ABE scheme.
+ *
+ * This wrapper handles base64 encoding of the plaintext/AAD, calls the Rust
+ * FFI, and returns base64-encoded ciphertext components.
+ *
+ * @param mpk Base64-encoded master public key.
+ * @param policy Policy string.
+ * @param plaintext Plaintext bytes to encrypt.
+ * @param aad Associated data bound to the symmetric encryption.
+ * @return EncryptOutput containing the base64-encoded ABE and symmetric
+ * ciphertexts.
+ * @throws std::runtime_error on error.
+ */
+EncryptOutput encrypt(const std::string &mpk, const std::string &policy,
+                      const std::vector<uint8_t> &plaintext,
+                      const std::vector<uint8_t> &aad);
+
+/**
+ * @brief Decrypts a hybrid ciphertext using the provided keys and AAD.
+ *
+ * This wrapper calls the Rust FFI and base64-decodes the recovered plaintext.
+ *
+ * @param usk Base64-encoded user secret key.
+ * @param gid Group identifier.
+ * @param policy Policy string.
+ * @param abe_ct Base64-encoded ABE ciphertext.
+ * @param sym_ct Base64-encoded symmetric ciphertext.
+ * @param aad Associated data bound to the symmetric encryption.
+ * @return Optional plaintext bytes on success, or std::nullopt on failure.
+ */
+std::optional<std::vector<uint8_t>>
+decrypt(const std::string &usk, const std::string &gid,
+        const std::string &policy, const std::string &abe_ct,
+        const std::string &sym_ct, const std::vector<uint8_t> &aad);
+} // namespace hybrid
+
 } // namespace accless::abe4

accless/libs/abe4/cpp-bindings/abe4.cpp

@@ -54,6 +54,31 @@ class Abe4ApiTest : public ::testing::Test {
 
         ASSERT_FALSE(decrypted_gt.has_value());
     }
+
+    void assert_hybrid_round_trip(
+        const std::vector<accless::abe4::UserAttribute> &user_attrs,
+        const std::string &policy, const std::string &plaintext,
+        const std::string &aad) {
+        auto auths = gather_authorities(user_attrs, policy);
+        accless::abe4::SetupOutput setup_output = accless::abe4::setup(auths);
+        std::string gid = "test_gid";
+        std::string usk_b64 =
+            accless::abe4::keygen(gid, setup_output.msk, user_attrs);
+
+        std::vector<uint8_t> plaintext_bytes(plaintext.begin(),
+                                             plaintext.end());
+        std::vector<uint8_t> aad_bytes(aad.begin(), aad.end());
+
+        auto hybrid_ct = accless::abe4::hybrid::encrypt(
+            setup_output.mpk, policy, plaintext_bytes, aad_bytes);
+        auto decrypted = accless::abe4::hybrid::decrypt(
+            usk_b64, gid, policy, hybrid_ct.abe_ciphertext,
+            hybrid_ct.sym_ciphertext, aad_bytes);
+
+        ASSERT_TRUE(decrypted.has_value());
+        std::string decrypted_str(decrypted->begin(), decrypted->end());
+        EXPECT_EQ(plaintext, decrypted_str);
+    }
 };
 
 TEST_F(Abe4ApiTest, SingleAuthSingleOk) {
@@ -190,3 +215,70 @@ TEST_F(Abe4ApiTest, SimpleNegationOk) {
     std::string policy = "!A.c:2";
     assert_decryption_ok(user_attrs, policy);
 }
+
+TEST_F(Abe4ApiTest, HybridRoundTripOk) {
+    std::vector<accless::abe4::UserAttribute> user_attrs = {
+        {"A", "a", "0"},
+        {"A", "c", "1"},
+    };
+    std::string policy = "A.a:0 & !A.c:0";
+    std::string plaintext = "hybrid plaintext payload";
+    std::string aad = "hybrid aad data";
+    assert_hybrid_round_trip(user_attrs, policy, plaintext, aad);
+}
+
+TEST_F(Abe4ApiTest, HybridDecryptFailsForUnauthorizedUser) {
+    std::vector<accless::abe4::UserAttribute> user_attrs = {};
+    std::string policy = "A.a:0";
+    std::string plaintext = "hybrid plaintext payload";
+    std::string aad = "hybrid aad data";
+
+    auto auths = gather_authorities(user_attrs, policy);
+    accless::abe4::SetupOutput setup_output = accless::abe4::setup(auths);
+    std::string gid = "test_gid";
+    std::string usk_b64 =
+        accless::abe4::keygen(gid, setup_output.msk, user_attrs);
+
+    std::vector<uint8_t> plaintext_bytes(plaintext.begin(), plaintext.end());
+    std::vector<uint8_t> aad_bytes(aad.begin(), aad.end());
+    auto hybrid_ct = accless::abe4::hybrid::encrypt(setup_output.mpk, policy,
+                                                    plaintext_bytes, aad_bytes);
+
+    auto decrypted = accless::abe4::hybrid::decrypt(
+        usk_b64, gid, policy, hybrid_ct.abe_ciphertext,
+        hybrid_ct.sym_ciphertext, aad_bytes);
+    ASSERT_FALSE(decrypted.has_value());
+}
+
+TEST_F(Abe4ApiTest, HybridRejectsModifiedAad) {
+    std::vector<accless::abe4::UserAttribute> user_attrs = {{"A", "a", "0"}};
+    std::string policy = "A.a:0";
+    std::string plaintext = "hybrid plaintext payload";
+    std::string aad = "hybrid aad data";
+    std::string wrong_aad = "tampered aad";
+
+    auto auths = gather_authorities(user_attrs, policy);
+    accless::abe4::SetupOutput setup_output = accless::abe4::setup(auths);
+    std::string gid = "test_gid";
+    std::string usk_b64 =
+        accless::abe4::keygen(gid, setup_output.msk, user_attrs);
+
+    std::vector<uint8_t> plaintext_bytes(plaintext.begin(), plaintext.end());
+    std::vector<uint8_t> aad_bytes(aad.begin(), aad.end());
+    std::vector<uint8_t> wrong_aad_bytes(wrong_aad.begin(), wrong_aad.end());
+
+    auto hybrid_ct = accless::abe4::hybrid::encrypt(setup_output.mpk, policy,
+                                                    plaintext_bytes, aad_bytes);
+
+    auto decrypted = accless::abe4::hybrid::decrypt(
+        usk_b64, gid, policy, hybrid_ct.abe_ciphertext,
+        hybrid_ct.sym_ciphertext, aad_bytes);
+    ASSERT_TRUE(decrypted.has_value());
+    std::string decrypted_str(decrypted->begin(), decrypted->end());
+    EXPECT_EQ(plaintext, decrypted_str);
+
+    auto tampered = accless::abe4::hybrid::decrypt(
+        usk_b64, gid, policy, hybrid_ct.abe_ciphertext,
+        hybrid_ct.sym_ciphertext, wrong_aad_bytes);
+    ASSERT_FALSE(tampered.has_value());
+}