| .. _module-pw_crypto: |
| |
| pw_crypto |
| ========= |
| A set of safe (read: easy to use, hard to misuse) crypto APIs. |
| |
| .. attention:: |
| |
| This module is under construction. |
| |
| The following crypto services are provided by this module. |
| |
| 1. Hashing a message with `SHA256`_. |
| 2. Verifying a digital signature signed with `ECDSA`_ over the NIST P256 curve. |
| 3. Many more to come ... |
| |
| SHA256 |
| ------ |
| |
| 1. Obtaining a oneshot digest. |
| |
| .. code-block:: cpp |
| |
| #include "pw_crypto/sha256.h" |
| |
| std::byte digest[32]; |
| Status status = pw::crypto::sha256::Hash(message, digest); |
| |
| 2. Hashing a long, potentially non-contiguous message. |
| |
| .. code-block:: cpp |
| |
| #include "pw_crypto/sha256.h" |
| |
| std::byte digest[32]; |
| auto h = pw::crypto::sha256::Sha256(); |
| |
| while (/* chunk ← Get next chunk of message */) { |
| h.Update(chunk); |
| } |
| |
| Status status = h.Final(digest); |
| |
| ECDSA |
| ----- |
| |
| 1. Verifying a digital signature signed with ECDSA over the NIST P256 curve. |
| |
| .. code-block:: cpp |
| |
| #include "pw_crypto/sha256.h" |
| |
| std::byte digest[32]; |
| auto status = pw::crypto::sha256::Hash(message, digest); |
| |
| if (!status.ok()) { |
| // handle errors. |
| } |
| |
| bool valid = pw::crypto::ecdsa::VerifyP256Signature(public_key, digest, signature).ok(); |
| |
| 2. Verifying a digital signature signed with ECDSA over the NIST P256 curve, with a long and/or non-contiguous message. |
| |
| .. code-block:: cpp |
| |
| #include "pw_crypto/sha256.h" |
| |
| std::byte digest[32]; |
| auto h = pw::crypto::sha256::Sha256(); |
| |
| while (/* chunk ← Get the next chunk of message */) { |
| h.Update(chunk); |
| } |
| |
| auto status = h.Final(digest); |
| bool valid = status.ok() && pw::crypto::ecdsa::VerifyP256Signature(public_key, digest, signature).ok(); |
| |
| Configuration |
| ------------- |
| |
| The crypto services offered by pw_crypto can be backed by different backend crypto libraries. For now only Mbed TLS is supported, others are under construction. |
| |
| Mbed TLS |
| ^^^^^^^^ |
| |
| To select the Mbed TLS backend, the MbedTLS library needs to be installed and configured. |
| |
| .. code-block:: sh |
| |
| # Install and configure MbedTLS |
| pw package install mbedtls |
| gn gen out --args='dir_pw_third_party_mbedtls="//.environment/packages/mbedtls" pw_crypto_SHA256_BACKEND="//pw_crypto:sha256_mbedtls" pw_crypto_ECDSA_BACKEND="//pw_crypto:ecdsa_mbedtls"' |
| |
| ninja -C out |
| |
| For optimal code size and/or performance, the Mbed TLS library needs to be configured per product. Mbed TLS configuration is achieved by turning on and off MBEDTLS_* options in a config.h file. See //third_party/mbedtls for how this is done. |
| |
| ``pw::crypto::sha256`` does not need any special configuration as it uses the mbedtls_sha256_* APIs directly. However you can optionally turn on ``MBEDTLS_SHA256_SMALLER`` to further reduce the code size to from 3KiB to ~1.8KiB at a ~30% slowdown cost (Cortex-M4). |
| |
| .. code-block:: c |
| |
| #define MBEDTLS_SHA256_SMALLER |
| |
| ``pw::crypto::ecdsa`` requires the following minimum configurations which yields a code size of ~12KiB. |
| |
| .. code-block:: c |
| |
| #define MBEDTLS_BIGNUM_C |
| #define MBEDTLS_ECP_C |
| #define MBEDTLS_ECDSA_C |
| // The ASN1 options are needed only because mbedtls considers and verifies |
| // them (in check_config.h) as dependencies of MBEDTLS_ECDSA_C. |
| #define MBEDTLS_ASN1_WRITE_C |
| #define MBEDTLS_ASN1_PARSE_C |
| #define MBEDTLS_ECP_NO_INTERNAL_RNG |
| #define MBEDTLS_ECP_DP_SECP256R1_ENABLED |
| |
| BoringSSL |
| ^^^^^^^^^ |
| |
| To select the BoringSSL backend, the BoringSSL library needs to be installed and configured. |
| |
| .. code-block:: sh |
| |
| # Install and configure BoringSSL |
| pw package install boringssl |
| gn gen out --args='dir_pw_third_party_boringssl="//.environment/packages/boringssl" pw_crypto_SHA256_BACKEND="//pw_crypto:sha256_boringssl"' |
| |
| ninja -C out |
| |
| Size Reports |
| ------------ |
| |
| Below are size reports for each crypto service. These vary across configurations. |
| |
| .. include:: size_report |