botan_hmac.cc

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// Copyright (C) 2011-2025 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#include <config.h>
 
#include <cryptolink.h>
#include <cryptolink/crypto_hmac.h>
 
#include <botan/mac.h>
#include <botan/mem_ops.h>
#include <botan/exceptn.h>
 
#include <cryptolink/botan_common.h>
 
namespace isc {
namespace cryptolink {
 
const std::string
btn::getHmacAlgorithmName(HashAlgorithm algorithm) {
    switch (algorithm) {
    case isc::cryptolink::MD5:
        return ("HMAC(MD5)");
    case isc::cryptolink::SHA1:
        return ("HMAC(SHA-1)");
    case isc::cryptolink::SHA256:
        return ("HMAC(SHA-256)");
    case isc::cryptolink::SHA224:
        return ("HMAC(SHA-224)");
    case isc::cryptolink::SHA384:
        return ("HMAC(SHA-384)");
    case isc::cryptolink::SHA512:
        return ("HMAC(SHA-512)");
    case isc::cryptolink::UNKNOWN_HASH:
        return ("HMAC(Unknown)");
    }
    // compiler should have prevented us to reach this, since we have
    // no default. But we need a return value anyway
    return ("Unknown");
}

class HMACImpl {
public:
    explicit HMACImpl(const void* secret, size_t secret_len,
                      const HashAlgorithm hash_algorithm)
    : hash_algorithm_(hash_algorithm), hmac_() {
        try {
            const std::string& name =
                btn::getHmacAlgorithmName(hash_algorithm);
            hmac_ = Botan::MessageAuthenticationCode::create_or_throw(name);
        } catch (const Botan::Lookup_Error&) {
            isc_throw(UnsupportedAlgorithm,
                      "Unknown hash algorithm: " <<
                      static_cast<int>(hash_algorithm));
        } catch (const Botan::Exception& exc) {
            isc_throw(LibraryError, "Botan error: " << exc.what());
        }
 
        try {
            // Botan 1.8 considers len 0 a bad key. 1.9 does not,
            // but we won't accept it anyway, and fail early
            if (secret_len == 0) {
                isc_throw(BadKey, "Bad HMAC secret length: 0");
            }
            hmac_->set_key(static_cast<const Botan::byte*>(secret),
                           secret_len);
        } catch (const Botan::Invalid_Key_Length& ikl) {
            isc_throw(BadKey, ikl.what());
        } catch (const Botan::Exception& exc) {
            isc_throw(LibraryError, "Botan error: " << exc.what());
        }
    }

    ~HMACImpl() = default;

    HashAlgorithm getHashAlgorithm() const {
        return (hash_algorithm_);
    }

    size_t getOutputLength() const {
        return (hmac_->output_length());
    }

    void update(const void* data, const size_t len) {
        try {
            hmac_->update(static_cast<const Botan::byte*>(data), len);
        } catch (const Botan::Exception& exc) {
            isc_throw(LibraryError, "Botan error: " << exc.what());
        }
    }

    void sign(isc::util::OutputBuffer& result, size_t len) {
        try {
            Botan::secure_vector<Botan::byte> b_result(hmac_->final());
 
            if (len > b_result.size()) {
                len = b_result.size();
            }
            result.writeData(&b_result[0], len);
        } catch (const Botan::Exception& exc) {
            isc_throw(LibraryError, "Botan error: " << exc.what());
        }
    }

    void sign(void* result, size_t len) {
        try {
            Botan::secure_vector<Botan::byte> b_result(hmac_->final());
            size_t output_size = getOutputLength();
            if (output_size > len) {
                output_size = len;
            }
            std::memcpy(result, &b_result[0], output_size);
        } catch (const Botan::Exception& exc) {
            isc_throw(LibraryError, "Botan error: " << exc.what());
        }
    }

    std::vector<uint8_t> sign(size_t len) {
        try {
            Botan::secure_vector<Botan::byte> b_result(hmac_->final());
            if (len > b_result.size()) {
                len = b_result.size();
            }
            // Return vector with content. Construct &b_result[len] attempts
            // to get an address of one element beyond the b_result. Replaced
            // with the address of first element + len
            return (std::vector<uint8_t>(&b_result[0], &b_result[0]+len));
        } catch (const Botan::Exception& exc) {
            isc_throw(LibraryError, "Botan error: " << exc.what());
        }
    }
 

    bool verify(const void* sig, size_t len) {
        // Botan's verify_mac checks if len matches the output_length,
        // which causes it to fail for truncated signatures, so we do
        // the check ourselves
        try {
            size_t size = getOutputLength();
            if (len < 10 || len < size / 2) {
                return (false);
            }
            if (len > size) {
                len = size;
            }
            if (digest_.size() == 0) {
                digest_ = hmac_->final();
            }
            const uint8_t* sig8 = static_cast<const uint8_t*>(sig);
            return (Botan::constant_time_compare(&digest_[0], sig8, len));
        } catch (const Botan::Exception& exc) {
            isc_throw(LibraryError, "Botan error: " << exc.what());
        }
    }
 
private:
    HashAlgorithm hash_algorithm_;

    std::unique_ptr<Botan::MessageAuthenticationCode> hmac_;

    Botan::secure_vector<Botan::byte> digest_;
};
 
HMAC::HMAC(const void* secret, size_t secret_length,
           const HashAlgorithm hash_algorithm)
{
    impl_ = new HMACImpl(secret, secret_length, hash_algorithm);
}
 
HMAC::~HMAC() {
    delete impl_;
}
 
HashAlgorithm
HMAC::getHashAlgorithm() const {
    return (impl_->getHashAlgorithm());
}
 
size_t
HMAC::getOutputLength() const {
    return (impl_->getOutputLength());
}
 
void
HMAC::update(const void* data, const size_t len) {
    impl_->update(data, len);
}
 
void
HMAC::sign(isc::util::OutputBuffer& result, size_t len) {
    impl_->sign(result, len);
}
 
void
HMAC::sign(void* result, size_t len) {
    impl_->sign(result, len);
}
 
std::vector<uint8_t>
HMAC::sign(size_t len) {
    return impl_->sign(len);
}
 
bool
HMAC::verify(const void* sig, const size_t len) {
    return (impl_->verify(sig, len));
}
 
} // namespace cryptolink
} // namespace isc