path: root/doc/manual/ffi.rst

FFI Interface
========================================

.. versionadded:: 1.11.14

Botan's ffi module provides a C89 API intended to be easily usable with other
language's foreign function interface (FFI) libraries. For instance the included
Python module uses the ``ctypes`` module for all library access. This API is of
course also useful for programs written directly in C.

Code examples can be found in `src/tests/test_ffi.cpp`.

Versioning
----------------------------------------

.. cpp:function:: uint32_t botan_ffi_api_version()

   Returns the version of the currently supported FFI API.  This is
   expressed in the form YYYYMMDD of the release date of this version
   of the API.

.. cpp:function:: int botan_ffi_supports_api(uint32_t version)

   Returns 0 iff the FFI version specified is supported by this
   library. Otherwise returns -1. The expression
   botan_ffi_supports_api(botan_ffi_api_version()) will always
   evaluate to 0. A particular version of the library may also support
   other (older) versions of the FFI API.

.. cpp:function:: const char* botan_version_string()

   Returns a free-from version string, e.g., 2.0.0

.. cpp:function:: uint32_t botan_version_major()

   Returns the major version of the library

.. cpp:function:: uint32_t botan_version_minor()

   Returns the minor version of the library

.. cpp:function:: uint32_t botan_version_patch()

   Returns the patch version of the library

.. cpp:function:: uint32_t botan_version_datestamp()

   Returns the date this version was released as an integer, or 0
   if an unreleased version

Utility Functions
----------------------------------------

.. cpp:function:: int botan_same_mem(const uint8_t* x, const uint8_t* y, size_t len)

   Returns 0 if `x[0..len] == y[0..len]`, -1 otherwise.

.. cpp:function:: int botan_hex_encode(const uint8_t* x, size_t len, char* out, uint32_t flags)

   Performs hex encoding of binary data in *x* of size *len* bytes.
   The output buffer *out* must be of at least *x*2* bytes in size.
   If *flags* contains ``BOTAN_FFI_HEX_LOWER_CASE``, hex encoding
   will only contain lower-case letters, upper-case letters otherwise.
   Returns 0 on success, 1 otherwise.

Random Number Generators
----------------------------------------

.. cpp:type:: opaque* botan_rng_t

   An opaque data type for a random number generator. Don't mess with it.

.. cpp:function:: int botan_rng_init(botan_rng_t* rng, const char* rng_type)

   Initialize a random number generator object from the given
   *rng_type*: "system" or `nullptr`: `System_RNG`, "user": `AutoSeeded_RNG`.

.. cpp:function:: int botan_rng_get(botan_rng_t rng, uint8_t* out, size_t out_len)

   Get random bytes from a random number generator.

.. cpp:function:: int botan_rng_reseed(botan_rng_t rng, size_t bits)

   Reseeds the random number generator with *bits* number of bits
   from the `System_RNG`.

.. cpp:function:: int botan_rng_destroy(botan_rng_t rng)

   Destroy the object created by :cpp:func:`botan_rng_init`.

Hash Functions
----------------------------------------

.. cpp:type:: opaque* botan_hash_t

   An opaque data type for a hash. Don't mess with it.

.. cpp:function:: botan_hash_t botan_hash_init(const char* hash, uint32_t flags)

   Creates a hash of the given name, e.g., "SHA-384".
   Returns null on failure. Flags should always be zero in this version of the API.

.. cpp:function:: int botan_hash_destroy(botan_hash_t hash)

   Destroy the object created by :cpp:func:`botan_hash_init`.

.. cpp:function:: int botan_hash_clear(botan_hash_t hash)

   Reset the state of this object back to clean, as if no input has
   been supplied.

.. cpp:function:: size_t botan_hash_output_length(botan_hash_t hash)

   Return the output length of the hash function.

.. cpp:function:: int botan_hash_update(botan_hash_t hash, const uint8_t* input, size_t len)

   Add input to the hash computation.

.. cpp:function:: int botan_hash_final(botan_hash_t hash, uint8_t out[])

   Finalize the hash and place the output in out. Exactly
   :cpp:func:`botan_hash_output_length` bytes will be written.

Message Authentication Codes
----------------------------------------
.. cpp:type:: opaque* botan_mac_t

    An opaque data type for a MAC. Don't mess with it, but do remember
    to set a random key first.

.. cpp:function:: botan_mac_t botan_mac_init(const char* mac, uint32_t flags)

   Creates a MAC of the given name, e.g., "HMAC(SHA-384)".
   Returns null on failure. Flags should always be zero in this version of the API.

.. cpp:function:: int botan_mac_destroy(botan_mac_t mac)

   Destroy the object created by :cpp:func:`botan_mac_init`.

.. cpp:function:: int botan_mac_clear(botan_mac_t mac)

   Reset the state of this object back to clean, as if no key and input have
   been supplied.

.. cpp:function:: size_t botan_mac_output_length(botan_mac_t mac)

   Return the output length of the MAC.

.. cpp:function:: int botan_mac_set_key(botan_mac_t mac, const uint8_t* key, size_t key_len)

   Set the random key.

.. cpp:function:: int botan_mac_update(botan_mac_t mac, uint8_t buf[], size_t len)

   Add input to the MAC computation.

.. cpp:function:: int botan_mac_final(botan_mac_t mac, uint8_t out[], size_t* out_len)

   Finalize the MAC and place the output in out. Exactly
   :cpp:func:`botan_mac_output_length` bytes will be written.

Ciphers
----------------------------------------

.. cpp:type:: opaque* botan_cipher_t

    An opaque data type for a MAC. Don't mess with it, but do remember
    to set a random key first. And please use an AEAD.

.. cpp:function:: botan_cipher_t botan_cipher_init(const char* cipher_name, uint32_t flags)

    Create a cipher object from a name such as "AES-256/GCM" or "Serpent/OCB".

    Flags is a bitfield
    The low bit of flags specifies if encrypt or decrypt

.. cpp:function:: int botan_cipher_destroy(botan_cipher_t cipher)

.. cpp:function:: int botan_cipher_clear(botan_cipher_t hash)

.. cpp:function:: int botan_cipher_set_key(botan_cipher_t cipher, \
                  const uint8_t* key, size_t key_len)

.. cpp:function:: int botan_cipher_set_associated_data(botan_cipher_t cipher, \
                                               const uint8_t* ad, size_t ad_len)

.. cpp:function:: int botan_cipher_start(botan_cipher_t cipher, \
                                 const uint8_t* nonce, size_t nonce_len)

.. cpp:function:: int botan_cipher_is_authenticated(botan_cipher_t cipher)

.. cpp:function:: size_t botan_cipher_tag_size(botan_cipher_t cipher)

.. cpp:function:: int botan_cipher_valid_nonce_length(botan_cipher_t cipher, size_t nl)

.. cpp:function:: size_t botan_cipher_default_nonce_length(botan_cipher_t cipher)

PBKDF
----------------------------------------

.. cpp:function:: int botan_pbkdf(const char* pbkdf_algo, \
                          uint8_t out[], size_t out_len, \
                          const char* passphrase, \
                          const uint8_t salt[], size_t salt_len, \
                          size_t iterations)

   Derive a key from a passphrase for a number of iterations
   using the given PBKDF algorithm, e.g., "PBKDF2".

.. cpp:function:: int botan_pbkdf_timed(const char* pbkdf_algo, \
                                uint8_t out[], size_t out_len, \
                                const char* passphrase, \
                                const uint8_t salt[], size_t salt_len, \
                                size_t milliseconds_to_run, \
                                size_t* out_iterations_used)

   Derive a key from a passphrase using the given PBKDF algorithm,
   e.g., "PBKDF2". If *out_iterations_used* is zero, instead the
   PBKDF is run until *milliseconds_to_run* milliseconds have passed.
   In this case, the number of iterations run will be written to
   *out_iterations_used*.

KDF
----------------------------------------

.. cpp:function:: int botan_kdf(const char* kdf_algo, \
                        uint8_t out[], size_t out_len, \
                        const uint8_t secret[], size_t secret_len, \
                        const uint8_t salt[], size_t salt_len, \
                        const uint8_t label[], size_t label_len)

   Derive a key using the given KDF algorithm, e.g., "SP800-56C".
   The derived key of length *out_len* bytes will be placed in *out*.

Multiple Precision Integers
----------------------------------------

.. versionadded: 2.1.0

.. cpp:type:: opaque* botan_mp_t

   An opaque data type for a multiple precision integer. Don't mess with it.

.. cpp:function:: int botan_mp_init(botan_mp_t* mp)

   Initialize a ``botan_mp_t``. Initial value is zero, use `botan_mp_set_X` to load a value.

.. cpp:function:: int botan_mp_destroy(botan_mp_t mp)

   Free a ``botan_mp_t``


.. cpp:function:: int botan_mp_to_hex(botan_mp_t mp, char* out)

   Writes exactly ``botan_mp_num_bytes(mp)*2 + 1`` bytes to out

.. cpp:function:: int botan_mp_to_str(botan_mp_t mp, uint8_t base, char* out, size_t* out_len)

   Base can be either 10 or 16.

.. cpp:function:: int botan_mp_set_from_int(botan_mp_t mp, int initial_value)

   Set ``botan_mp_t`` from an integer value.

.. cpp:function:: int botan_mp_set_from_mp(botan_mp_t dest, botan_mp_t source)

   Set ``botan_mp_t`` from another MP.

.. cpp:function:: int botan_mp_set_from_str(botan_mp_t dest, const char* str)

   Set ``botan_mp_t`` from a string. Leading prefix of "0x" is accepted.

.. cpp:function:: int botan_mp_num_bits(botan_mp_t n, size_t* bits)

   Return the size of ``n`` in bits.

.. cpp:function:: int botan_mp_num_bytes(botan_mp_t n, size_t* bytes)

   Return the size of ``n`` in bytes.

.. cpp:function:: int botan_mp_to_bin(botan_mp_t mp, uint8_t vec[])

   Writes exactly ``botan_mp_num_bytes(mp)`` to ``vec``.

.. cpp:function:: int botan_mp_from_bin(botan_mp_t mp, const uint8_t vec[], size_t vec_len)

   Loads ``botan_mp_t`` from a binary vector (as produced by ``botan_mp_to_bin``).

.. cpp:function:: int botan_mp_is_negative(botan_mp_t mp)

   Return 1 if ``mp`` is negative, otherwise 0.

.. cpp:function:: int botan_mp_flip_sign(botan_mp_t mp)

   Flip the sign of ``mp``.

.. cpp:function:: int botan_mp_add(botan_mp_t result, botan_mp_t x, botan_mp_t y)

   Add two ``botan_mp_t``s and store the output in ``result``.

.. cpp:function:: int botan_mp_sub(botan_mp_t result, botan_mp_t x, botan_mp_t y)

   Subtract two ``botan_mp_t``s and store the output in ``result``.

.. cpp:function:: int botan_mp_mul(botan_mp_t result, botan_mp_t x, botan_mp_t y)

   Multiply two ``botan_mp_t``s and store the output in ``result``.

.. cpp:function:: int botan_mp_div(botan_mp_t quotient, botan_mp_t remainder, \
                           botan_mp_t x, botan_mp_t y)

   Divide ``x`` by ``y`` and store the output in ``quotient`` and ``remainder``.

.. cpp:function:: int botan_mp_mod_mul(botan_mp_t result, botan_mp_t x, botan_mp_t y, botan_mp_t mod)

   Set ``result`` to ``x`` times ``y`` modulo ``mod``.

.. cpp:function:: int botan_mp_equal(botan_mp_t x, botan_mp_t y)

   Return 1 if ``x`` is equal to ``y``, 0 if ``x`` is not equal to ``y``

.. cpp:function:: int botan_mp_cmp(int* result, botan_mp_t x, botan_mp_t y)

   Three way comparison: set result to -1 if ``x`` is less than ``y``,
   0 if ``x`` is equal to ``y``, and 1 if ``x`` is greater than ``y``.

.. cpp:function:: int botan_mp_swap(botan_mp_t x, botan_mp_t y)

   Swap two ``botan_mp_t`` values.

.. cpp:function:: int botan_mp_powmod(botan_mp_t out, botan_mp_t base, botan_mp_t exponent, botan_mp_t modulus)

   Modular exponentiation.

.. cpp:function:: int botan_mp_lshift(botan_mp_t out, botan_mp_t in, size_t shift)

   Left shift by specified bit count, place result in ``out``.

.. cpp:function:: int botan_mp_rshift(botan_mp_t out, botan_mp_t in, size_t shift)

   Right shift by specified bit count, place result in ``out``.

.. cpp:function:: int botan_mp_mod_inverse(botan_mp_t out, botan_mp_t in, botan_mp_t modulus)

   Compute modular inverse. If no modular inverse exists (for instance because ``in`` and
   ``modulus`` are not relatively prime), then sets ``out`` to -1.

.. cpp:function:: int botan_mp_rand_bits(botan_mp_t rand_out, botan_rng_t rng, size_t bits)

   Create a random ``botan_mp_t`` of the specified bit size.

.. cpp:function:: int botan_mp_rand_range(botan_mp_t rand_out, botan_rng_t rng, \
                                  botan_mp_t lower_bound, botan_mp_t upper_bound)

   Create a random ``botan_mp_t`` within the provided range.

.. cpp:function:: int botan_mp_gcd(botan_mp_t out, botan_mp_t x, botan_mp_t y)

   Compute the greated common divisor of ``x`` and ``y``.

.. cpp:function:: int botan_mp_is_prime(botan_mp_t n, botan_rng_t rng, size_t test_prob)

   Test if ``n`` is prime. The algorithm used (Miller-Rabin) is probabalistic,
   set ``test_prob`` to the desired assurance level. For example if
   ``test_prob`` is 64, then sufficient Miller-Rabin iterations will run to
   assure there is at most a ``1/2**64`` chance that ``n`` is composit.

.. cpp:function:: int botan_mp_bit_set(botan_mp_t n, size_t bit)

   Returns 0 if the specified bit of ``n`` is not set, 1 if it is set.


Password Hashing
----------------------------------------

.. cpp:function:: int botan_bcrypt_generate(uint8_t* out, size_t* out_len, \
                                    const char* password, \
                                    botan_rng_t rng, \
                                    size_t work_factor, \
                                    uint32_t flags)

   Create a password hash using Bcrypt.
   The output buffer *out* should be of length 64 bytes.
   The output is formatted bcrypt $2a$...

.. cpp:function:: int botan_bcrypt_is_valid(const char* pass, const char* hash)

   Check a previously created password hash.
   Returns 0 if if this password/hash combination is valid,
   1 if the combination is not valid (but otherwise well formed),
   negative on error.

Public Key Creation, Import and Export
----------------------------------------

.. cpp:type:: opaque* botan_privkey_t

   An opaque data type for a private key. Don't mess with it.

.. cpp:function:: int botan_privkey_create(botan_privkey_t* key, \
                                   const char* algo_name, \
                                   const char* algo_params, \
                                   botan_rng_t rng)

.. cpp:function:: int botan_privkey_create_rsa(botan_privkey_t* key, botan_rng_t rng, size_t n_bits)

.. cpp:function:: int botan_privkey_create_ecdsa(botan_privkey_t* key, botan_rng_t rng, const char* params)

.. cpp:function:: int botan_privkey_create_ecdh(botan_privkey_t* key, botan_rng_t rng, const char* params)

.. cpp:function:: int botan_privkey_create_mceliece(botan_privkey_t* key, botan_rng_t rng, size_t n, size_t t)

.. cpp:function:: int botan_privkey_load(botan_privkey_t* key, botan_rng_t rng, \
                                 const uint8_t bits[], size_t len, \
                                 const char* password)

.. cpp:function:: int botan_privkey_destroy(botan_privkey_t key)

.. cpp:function:: int botan_privkey_export(botan_privkey_t key, \
                                   uint8_t out[], size_t* out_len, \
                                   uint32_t flags)

.. cpp:function:: int botan_privkey_export_encrypted(botan_privkey_t key, \
                                             uint8_t out[], size_t* out_len, \
                                             botan_rng_t rng, \
                                             const char* passphrase, \
                                             const char* encryption_algo, \
                                             uint32_t flags)

.. cpp:type:: opaque* botan_pubkey_t

   An opaque data type for a public key. Don't mess with it.

.. cpp:function:: int botan_pubkey_load(botan_pubkey_t* key, const uint8_t bits[], size_t len)

.. cpp:function:: int botan_privkey_export_pubkey(botan_pubkey_t* out, botan_privkey_t in)

.. cpp:function:: int botan_pubkey_export(botan_pubkey_t key, uint8_t out[], size_t* out_len, uint32_t flags)

.. cpp:function:: int botan_pubkey_algo_name(botan_pubkey_t key, char out[], size_t* out_len)

.. cpp:function:: int botan_pubkey_estimated_strength(botan_pubkey_t key, size_t* estimate)

.. cpp:function:: int botan_pubkey_fingerprint(botan_pubkey_t key, const char* hash, \
                                       uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_pubkey_destroy(botan_pubkey_t key)

RSA specific functions
----------------------------------------

.. cpp:function:: int botan_privkey_rsa_get_p(botan_mp_t p, botan_privkey_t rsa_key)

   Set ``p`` to the first RSA prime.

.. cpp:function:: int botan_privkey_rsa_get_q(botan_mp_t q, botan_privkey_t rsa_key)

   Set ``q`` to the second RSA prime.

.. cpp:function:: int botan_privkey_rsa_get_d(botan_mp_t d, botan_privkey_t rsa_key)

   Set ``d`` to the RSA private exponent.

.. cpp:function:: int botan_privkey_rsa_get_n(botan_mp_t n, botan_privkey_t rsa_key)

   Set ``n`` to the RSA modulus.

.. cpp:function:: int botan_privkey_rsa_get_e(botan_mp_t e, botan_privkey_t rsa_key)

   Set ``e`` to the RSA public exponent.

.. cpp:function:: int botan_pubkey_rsa_get_e(botan_mp_t e, botan_pubkey_t rsa_key)

   Set ``e`` to the RSA public exponent.

.. cpp:function:: int botan_pubkey_rsa_get_n(botan_mp_t n, botan_pubkey_t rsa_key)

   Set ``n`` to the RSA modulus.

.. cpp:function:: int botan_privkey_load_rsa(botan_privkey_t* key, \
                                     botan_mp_t p, botan_mp_t q, botan_mp_t d)

   Initialize a private RSA key using parameters p, q, and d.

.. cpp:function:: int botan_pubkey_load_rsa(botan_pubkey_t* key, \
                                    botan_mp_t n, botan_mp_t e)

   Initialize a public RSA key using parameters n and e.


Public Key Encryption/Decryption
----------------------------------------

.. cpp:type:: opaque* botan_pk_op_encrypt_t

   An opaque data type for an encryption operation. Don't mess with it.

.. cpp:function:: int botan_pk_op_encrypt_create(botan_pk_op_encrypt_t* op, \
                                         botan_pubkey_t key, \
                                         const char* padding, \
                                         uint32_t flags)

.. cpp:function:: int botan_pk_op_encrypt_destroy(botan_pk_op_encrypt_t op)

.. cpp:function:: int botan_pk_op_encrypt(botan_pk_op_encrypt_t op, \
                                  botan_rng_t rng, \
                                  uint8_t out[], size_t* out_len, \
                                  const uint8_t plaintext[], size_t plaintext_len)

.. cpp:type:: opaque* botan_pk_op_decrypt_t

   An opaque data type for a decryption operation. Don't mess with it.

.. cpp:function:: int botan_pk_op_decrypt_create(botan_pk_op_decrypt_t* op, \
                                         botan_privkey_t key, \
                                         const char* padding, \
                                         uint32_t flags)

.. cpp:function:: int botan_pk_op_decrypt_destroy(botan_pk_op_decrypt_t op)

.. cpp:function:: int botan_pk_op_decrypt(botan_pk_op_decrypt_t op, \
                                  uint8_t out[], size_t* out_len, \
                                  uint8_t ciphertext[], size_t ciphertext_len)

Signatures
----------------------------------------

.. cpp:type:: opaque* botan_pk_op_sign_t

   An opaque data type for a signature generation operation. Don't mess with it.

.. cpp:function:: int botan_pk_op_sign_create(botan_pk_op_sign_t* op, \
                                      botan_privkey_t key, \
                                      const char* hash_and_padding, \
                                      uint32_t flags)

.. cpp:function:: int botan_pk_op_sign_destroy(botan_pk_op_sign_t op)

.. cpp:function:: int botan_pk_op_sign_update(botan_pk_op_sign_t op, \
                                      const uint8_t in[], size_t in_len)

.. cpp:function:: int botan_pk_op_sign_finish(botan_pk_op_sign_t op, botan_rng_t rng, \
                                      uint8_t sig[], size_t* sig_len)

.. cpp:type:: opaque* botan_pk_op_verify_t

   An opaque data type for a signature verification operation. Don't mess with it.

.. cpp:function:: int botan_pk_op_verify_create(botan_pk_op_verify_t* op, \
                                        botan_pubkey_t key, \
                                        const char* hash_and_padding, \
                                        uint32_t flags)

.. cpp:function:: int botan_pk_op_verify_destroy(botan_pk_op_verify_t op)

.. cpp:function:: int botan_pk_op_verify_update(botan_pk_op_verify_t op, \
                                        const uint8_t in[], size_t in_len)

.. cpp:function:: int botan_pk_op_verify_finish(botan_pk_op_verify_t op, \
                                        const uint8_t sig[], size_t sig_len)

Key Agreement
----------------------------------------

.. cpp:type:: opaque* botan_pk_op_ka_t

   An opaque data type for a key agreement operation. Don't mess with it.

.. cpp:function:: int botan_pk_op_key_agreement_create(botan_pk_op_ka_t* op, \
                                               botan_privkey_t key, \
                                               const char* kdf, \
                                               uint32_t flags)

.. cpp:function:: int botan_pk_op_key_agreement_destroy(botan_pk_op_ka_t op)

.. cpp:function:: int botan_pk_op_key_agreement_export_public(botan_privkey_t key, \
                                                      uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_pk_op_key_agreement(botan_pk_op_ka_t op, \
                                        uint8_t out[], size_t* out_len, \
                                        const uint8_t other_key[], size_t other_key_len, \
                                        const uint8_t salt[], size_t salt_len)

.. cpp:function:: int botan_mceies_encrypt(botan_pubkey_t mce_key, \
                                   botan_rng_t rng, \
                                   const char* aead, \
                                   const uint8_t pt[], size_t pt_len, \
                                   const uint8_t ad[], size_t ad_len, \
                                   uint8_t ct[], size_t* ct_len)

.. cpp:function:: int botan_mceies_decrypt(botan_privkey_t mce_key, \
                                   const char* aead, \
                                   const uint8_t ct[], size_t ct_len, \
                                   const uint8_t ad[], size_t ad_len, \
                                   uint8_t pt[], size_t* pt_len)

X.509 Certificates
----------------------------------------

.. cpp:type:: opaque* botan_x509_cert_t

   An opaque data type for an X.509 certificate. Don't mess with it.

.. cpp:function:: int botan_x509_cert_load(botan_x509_cert_t* cert_obj, \
                                        const uint8_t cert[], size_t cert_len)

.. cpp:function:: int botan_x509_cert_load_file(botan_x509_cert_t* cert_obj, const char* filename)

.. cpp:function:: int botan_x509_cert_destroy(botan_x509_cert_t cert)

.. cpp:function:: int botan_x509_cert_gen_selfsigned(botan_x509_cert_t* cert, \
                                             botan_privkey_t key, \
                                             botan_rng_t rng, \
                                             const char* common_name, \
                                             const char* org_name)

.. cpp:function:: int botan_x509_cert_get_time_starts(botan_x509_cert_t cert, char out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_get_time_expires(botan_x509_cert_t cert, char out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_get_fingerprint(botan_x509_cert_t cert, const char* hash, uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_get_serial_number(botan_x509_cert_t cert, uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_get_authority_key_id(botan_x509_cert_t cert, uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_get_subject_key_id(botan_x509_cert_t cert, uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_path_verify(botan_x509_cert_t cert, \
                                          const char* ca_dir)

.. cpp:function:: int botan_x509_cert_get_public_key_bits(botan_x509_cert_t cert, \
                                                  uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_get_public_key(botan_x509_cert_t cert, botan_pubkey_t* key)

.. cpp:function:: int botan_x509_cert_get_issuer_dn(botan_x509_cert_t cert, \
                                            const char* key, size_t index, \
                                            uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_get_subject_dn(botan_x509_cert_t cert, \
                                             const char* key, size_t index, \
                                             uint8_t out[], size_t* out_len)

.. cpp:function:: int botan_x509_cert_to_string(botan_x509_cert_t cert, char out[], size_t* out_len)

.. cpp:enum:: botan_x509_cert_key_constraints

   Certificate key usage constraints. Allowed values: `NO_CONSTRAINTS`,
   `DIGITAL_SIGNATURE`, `NON_REPUDIATION`, `KEY_ENCIPHERMENT`,
   `DATA_ENCIPHERMENT`, `KEY_AGREEMENT`, `KEY_CERT_SIGN`,
   `CRL_SIGN`, `ENCIPHER_ONLY`, `DECIPHER_ONLY`.

.. cpp:function:: int botan_x509_cert_allowed_usage(botan_x509_cert_t cert, unsigned int key_usage)