# Botan

# Python Binding

Added in version 1.11.14.

The Python binding is based on the ffi module of botan and the ctypes module of the Python standard library.

The versioning of the Python module follows the major versioning of the C++ library. So for Botan 2, the module is named `botan2` while for Botan 3 it is `botan3`.

## Versioning

botan3.version_major()

  Returns the major number of the library version.

botan3.version_minor()

  Returns the minor number of the library version.

botan3.version_patch()

  Returns the patch number of the library version.

botan3.version_string()

  Returns a free form version string for the library

## Random Number Generators

class botan3.RandomNumberGenerator(rng_type='system')

  > Previously `rng`

  > Type ‘user’ also allowed (userspace HMAC_DRBG seeded from system rng). The system RNG is very cheap to create, as just a single file handle or CSP handle is kept open, from first use until shutdown, no matter how many ‘system’ rng instances are created. Thus it is easy to use the RNG in a one-off way, with botan.RandomNumberGenerator().get(32).

  > For some use cases it can be useful to provide a custom RNG implementation. Use ‘custom’ as the rng_type and provide the `get_callback=` and `add_entropy_callback=` arguments. The latter is optional. `get_callback` takes an integer and is expected to return a bytes object with the requested number of random bytes. `add_entropy_callback` takes a bytes object containing entropy bytes and is expected to add the given entropy to the RNG.

  > When Botan is configured with TPM 2.0 support, also ‘tpm2’ is allowed to instantiate a TPM-backed RNG. Note that this requires passing additional named arguments `tpm2_context=` with a `TPM2Context` and (optionally) `tpm2_sessions=` with one or more `TPM2Session` objects.

  get(length)

    Return some bytes

  reseed(bits=256)

    Meaningless on system RNG, on userspace RNG causes a reseed/rekey

  reseed_from_rng(source_rng, bits=256)

    Take bits from the source RNG and use it to seed `self`

  add_entropy(seed)

    Add some unpredictable seed data to the RNG

## Hash Functions

class botan3.HashFunction(algo)

  Previously `hash_function`

  The `algo` param is a string (eg ‘SHA-1’, ‘SHA-384’, ‘BLAKE2b’)

  algo_name()

    Returns the name of this algorithm

  clear()

    Clear state

  output_length()

    Return output length in bytes

  update(x)

    Add some input

  final()

    Returns the hash of all input provided, resets for another message.

## Message Authentication Codes

class botan3.MsgAuthCode(algo)

  Previously `message_authentication_code`

  Algo is a string (eg ‘HMAC(SHA-256)’, ‘Poly1305’, ‘CMAC(AES-256)’)

  algo_name()

    Returns the name of this algorithm

  clear()

    Clear internal state including the key

  output_length()

    Return the output length in bytes

  set_key(key)

    Set the key

  update(x)

    Add some input

  final()

    Returns the MAC of all input provided, resets for another message with the same key.

## Ciphers

class botan3.SymmetricCipher(object, algo, encrypt=True)

  > Previously `cipher`

  > The algorithm is specified as a string (eg ‘AES-128/GCM’, ‘Serpent/OCB(12)’, ‘Threefish-512/EAX’).

  > Set the second param to False for decryption

  algo_name()

    Returns the name of this algorithm

  tag_length()

    Returns the tag length (0 for unauthenticated modes)

  default_nonce_length()

    Returns default nonce length

  update_granularity()

    Returns update block size. Call to update() must provide input of exactly this many bytes

  is_authenticated()

    Returns True if this is an AEAD mode

  valid_nonce_length(nonce_len)

    Returns True if nonce_len is a valid nonce len for this mode

  clear()

    Resets all state

  set_key(key)

    Set the key

  set_assoc_data(ad)

    Sets the associated data. Fails if this is not an AEAD mode

  start(nonce)

    Start processing a message using nonce

  update(txt)

    Consumes input text and returns output. Input text must be of update_granularity() length. Alternately, always call finish with the entire message, avoiding calls to update entirely

  finish(txt=None)

    Finish processing (with an optional final input). May throw if message authentication checks fail, in which case all plaintext previously processed must be discarded. You may call finish() with the entire message

## Bcrypt

botan3.bcrypt(passwd, rng, work_factor=10)

  Provided the password and an RNG object, returns a bcrypt string

botan3.check_bcrypt(passwd, bcrypt)

  Check a bcrypt hash against the provided password, returning True iff the password matches.

## PBKDF

botan3.pbkdf(algo, password, out_len, iterations=100000, salt=None)

  Runs a PBKDF2 algo specified as a string (eg ‘PBKDF2(SHA-256)’, ‘PBKDF2(CMAC(Blowfish))’). Runs with specified iterations, with meaning depending on the algorithm. The salt can be provided or otherwise is randomly chosen. In any case it is returned from the call.

  Returns out_len bytes of output (or potentially less depending on the algorithm and the size of the request).

  Returns tuple of salt, iterations, and psk

botan3.pbkdf_timed(algo, password, out_len, ms_to_run=300, salt=rng().get(12))

  Runs for as many iterations as needed to consumed ms_to_run milliseconds on whatever we’re running on. Returns tuple of salt, iterations, and psk

## Scrypt

Added in version 2.8.0.

botan3.scrypt(out_len, password, salt, N=1024, r=8, p=8)

  Runs Scrypt key derivation function over the specified password and salt using Scrypt parameters N, r, p.

## KDF

botan3.kdf(algo, secret, out_len, salt)

  Performs a key derviation function (such as “HKDF(SHA-384)”) over the provided secret and salt values. Returns a value of the specified length.

## Public Key

class botan3.PublicKey(object)

  Previously `public_key`

  classmethod load(val)

    Load a public key. The value should be a PEM or DER blob.

  classmethod load_rsa(n, e)

    Load an RSA public key giving the modulus and public exponent as integers.

  classmethod load_dsa(p, q, g, y)

    Load an DSA public key giving the parameters and public value as integers.

  classmethod load_dh(p, g, y)

    Load an Diffie-Hellman public key giving the parameters and public value as integers.

  classmethod load_elgamal(p, q, g, y)

    Load an ElGamal public key giving the parameters and public value as integers.

  classmethod load_ecdsa(curve, pub_x, pub_y)

    Load an ECDSA public key giving the curve as a string (like “secp256r1”) and the public point as a pair of integers giving the affine coordinates.

  classmethod load_ecdh(curve, pub_x, pub_y)

    Load an ECDH public key giving the curve as a string (like “secp256r1”) and the public point as a pair of integers giving the affine coordinates.

  classmethod load_sm2(curve, pub_x, pub_y)

    Load a SM2 public key giving the curve as a string (like “sm2p256v1”) and the public point as a pair of integers giving the affine coordinates.

  classmethod load_ml_kem(mode, raw_encoding)

    Load an ML-KEM public key giving the mode as a string (like “ML-KEM-512”) and the raw encoding of the public key.

  classmethod load_ml_dsa(mode, raw_encoding)

    Load an ML-DSA public key giving the mode as a string (like “ML-DSA-4x4”) and the raw encoding of the public key.

  classmethod load_slh_dsa(mode, raw_encoding)

    Load an SLH-DSA public key giving the mode as a string (like “SLH-DSA-SHAKE-128f”) and the raw encoding of the public key.

  check_key(rng_obj, strong=True):

    Test the key for consistency. If `strong` is `True` then more expensive tests are performed.

  export(pem=False)

    Exports the public key using the usual X.509 SPKI representation. If `pem` is True, the result is a PEM encoded string. Otherwise it is a binary DER value.

  to_der()

    Like `self.export(False)`

  to_pem()

    Like `self.export(True)`

  to_raw()

    Exports the key in its canonical raw encoding. This might not be available for all key types and raise an exception in that case.

  get_field(field_name)

    Return an integer field related to the public key. The valid field names vary depending on the algorithm. For example RSA public modulus can be extracted with `rsa_key.get_field("n")`.

  object_identifier()

    Returns the associated OID

  fingerprint(hash='SHA-256')

    Returns a hash of the public key

  algo_name()

    Returns the algorithm name

  estimated_strength()

    Returns the estimated strength of this key against known attacks (NFS, Pollard’s rho, etc)

## Private Key

class botan3.PrivateKey

  Previously `private_key`

  classmethod create(algo, param, rng)

    Creates a new private key. The parameter type/value depends on the algorithm. For “rsa” is is the size of the key in bits. For “ecdsa” and “ecdh” it is a group name (for instance “secp256r1”). For “ecdh” there is also a special case for groups “curve25519” and “x448” (which are actually completely distinct key types with a non-standard encoding).

  classmethod create_ec(algo, ec_group, rng)

    Creates a new ec private key.

  classmethod load(val, passphrase='')

    Return a private key (DER or PEM formats accepted)

  classmethod load_rsa(p, q, e)

    Return a private RSA key

  classmethod load_dsa(p, q, g, x)

    Return a private DSA key

  classmethod load_dh(p, g, x)

    Return a private DH key

  classmethod load_elgamal(p, q, g, x)

    Return a private ElGamal key

  classmethod load_ecdsa(curve, x)

    Return a private ECDSA key

  classmethod load_ecdh(curve, x)

    Return a private ECDH key

  classmethod load_sm2(curve, x)

    Return a private SM2 key

  classmethod load_ml_kem(mode, raw_encoding)

    Return a private ML-KEM key

  classmethod load_ml_dsa(mode, raw_encoding)

    Return a private ML-DSA key

  classmethod load_slh_dsa(mode, raw_encoding)

    Return a private SLH-DSA key

  get_public_key()

    Return a public_key object

  to_pem()

    Return the PEM encoded private key (unencrypted). Like `self.export(True)`

  to_der()

    Return the PEM encoded private key (unencrypted). Like `self.export(False)`

  to_raw()

    Exports the key in its canonical raw encoding. This might not be available for all key types and raise an exception in that case.

  check_key(rng_obj, strong=True):

    Test the key for consistency. If `strong` is `True` then more expensive tests are performed.

  algo_name()

    Returns the algorithm name

  export(pem=False)

    Exports the private key in PKCS8 format. If `pem` is True, the result is a PEM encoded string. Otherwise it is a binary DER value. The key will not be encrypted.

  export_encrypted(passphrase, rng, pem=False, msec=300, cipher=None, pbkdf=None)

    Exports the private key in PKCS8 format, encrypted using the provided passphrase. If `pem` is True, the result is a PEM encoded string. Otherwise it is a binary DER value.

  get_field(field_name)

    Return an integer field related to the public key. The valid field names vary depending on the algorithm. For example first RSA secret prime can be extracted with `rsa_key.get_field("p")`. This function can also be used to extract the public parameters.

  object_identifier()

    Returns the associated OID

  stateful_operation()
  Return whether the key is stateful or not.
  remaining_operations()
  If the key is stateful, return the number of remaining operations.
  Raises an exception if the key is not stateful.

## Public Key Operations

class botan3.PKEncrypt(pubkey, padding)

  Previously `pk_op_encrypt`

  encrypt(msg, rng)

class botan3.PKDecrypt(privkey, padding)

  Previously `pk_op_decrypt`

  decrypt(msg)

class botan3.PKSign(privkey, hash_w_padding)

  Previously `pk_op_sign`

  update(msg)
  finish(rng)

class botan3.PKVerify(pubkey, hash_w_padding)

  Previously `pk_op_verify`

  update(msg)
  check_signature(signature)

class botan3.PKKeyAgreement(privkey, kdf)

  Previously `pk_op_key_agreement`

  public_value()

  Returns the public value to be passed to the other party

  agree(other, key_len, salt)

  Returns a key derived by the KDF.

## TPM 2.0 Bindings

Added in version 3.6.0.

class botan3.TPM2Context(tcti_nameconf=None, tcti_conf=None)

  Create a TPM 2.0 context optionally with a TCTI name and configuration, separated by a colon, or as separate parameters.

  supports_botan_crypto_backend()

  Returns True if the TPM adapter can use Botan-based crypto primitives to communicate with the TPM

  enable_botan_crypto_backend(rng)

  Enables the TPM adapter to use Botan-based crypto primitives. The passed RNG must not depend on the TPM itself.

class botan3.TPM2UnauthenticatedSession(ctx)

  Creates a TPM 2.0 session that is not bound to any authentication credential but provides basic parameter encryption between the TPM and the application.

## Multiple Precision Integers (MPI)

Added in version 2.8.0.

class botan3.MPI(initial_value=None, radix=None)

  Initialize an MPI object with specified value, left as zero otherwise. The `initial_value` should be an `int`, `str`, or `MPI`. The `radix` value should be set to 16 when initializing from a base 16 str value.

  Most of the usual arithmetic operators (`__add__`, `__mul__`, etc) are defined.

  inverse_mod(modulus)

    Return the inverse of `self` modulo `modulus`, or zero if no inverse exists

  is_prime(rng, prob=128)

    Test if `self` is prime

  pow_mod(exponent, modulus):

    Return `self` to the `exponent` power modulo `modulus`

  mod_mul(other, modulus):

    Return the multiplication product of `self` and `other` modulo `modulus`

  gcd(other):

    Return the greatest common divisor of `self` and `other`

## Object Identifiers (OID)

Added in version 3.8.0.

class botan3.OID(object)
  classmethod from_string(value)

    Create a new OID from dot notation or from a known name

  to_string()

    Export the OID in dot notation

  to_name()

    Export the OID as a name if it has one, else in dot notation

  register(name)

    Register the OID so that it may later be retrieved by the given name

## EC Groups

Added in version 3.8.0.

class botan3.ECGroup(object)
  classmethod supports_application_specific_group()

    Returns true if in this build configuration it is possible to register an application specific elliptic curve

  classmethod supports_named_group(name)

    Returns true if in this build configuration ECGroup.from_name(name) will succeed

  classmethod from_params(oid, p, a, b, base_x, base_y, order)

    Creates a new ECGroup from ec parameters

  classmethod from_ber(ber)

    Creates a new ECGroup from a BER blob

  classmethod from_pem(pem)

    Creates a new ECGroup from a pem encoding

  classmethod from_oid(oid)

    Creates a new ECGroup from a group named by an OID

  classmethod from_name(name)

    Creates a new ECGroup from a common group name

  to_der()

    Export the group in DER encoding

  to_pem()

    Export the group in PEM encoding

  get_curve_oid()

    Get the curve OID

  get_p()

    Get the prime modulus of the field

  get_a()

    Get the a parameter of the elliptic curve equation

  get_b()

    Get the b parameter of the elliptic curve equation

  get_g_x()

    Get the x coordinate of the base point

  get_g_y()

    Get the y coordinate of the base point

  get_order()

    Get the order of the base point

## Format Preserving Encryption (FE1 scheme)

Added in version 2.8.0.

class botan3.FormatPreservingEncryptionFE1(modulus, key, rounds=5, compat_mode=False)

  Initialize an instance for format preserving encryption

  encrypt(msg, tweak)

    The msg should be a botan3.MPI or an object which can be converted to one

  decrypt(msg, tweak)

    The msg should be a botan3.MPI or an object which can be converted to one

## HOTP

Added in version 2.8.0.

class botan3.HOTP(key, hash='SHA-1', digits=6)
  generate(counter)

    Generate an HOTP code for the provided counter

  check(code, counter, resync_range=0)

    Check if provided `code` is the correct code for `counter`. If `resync_range` is greater than zero, HOTP also checks up to `resync_range` following counter values.

    Returns a tuple of (bool,int) where the boolean indicates if the code was valid, and the int indicates the next counter value that should be used. If the code did not verify, the next counter value is always identical to the counter that was passed in. If the code did verify and resync_range was zero, then the next counter will always be counter+1.

## X509Cert

class botan3.X509Cert(filename=None, buf=None)
  time_starts()

    Return the time the certificate becomes valid, as a string in form “YYYYMMDDHHMMSSZ” where Z is a literal character reflecting that this time is relative to UTC.

  time_expires()

    Return the time the certificate expires, as a string in form “YYYYMMDDHHMMSSZ” where Z is a literal character reflecting that this time is relative to UTC.

  to_string()

    Format the certificate as a free-form string.

  fingerprint(hash_algo='SHA-256')

    Return a fingerprint for the certificate, which is basically just a hash of the binary contents. Normally SHA-1 or SHA-256 is used, but any hash function is allowed.

  serial_number()

    Return the serial number of the certificate.

  authority_key_id()

    Return the authority key ID set in the certificate, which may be empty.

  subject_key_id()

    Return the subject key ID set in the certificate, which may be empty.

  subject_public_key_bits()

    Get the serialized representation of the public key included in this certificate.

  subject_public_key()

    Get the public key included in this certificate as an object of class `PublicKey`.

  subject_dn(key, index)

    Get a value from the subject DN field.

    `key` specifies a value to get, for instance `"Name"` or “Country”.

  issuer_dn(key, index)

    Get a value from the issuer DN field.

    `key` specifies a value to get, for instance `"Name"` or “Country”.

  hostname_match(hostname)

    Return True if the Common Name (CN) field of the certificate matches a given `hostname`.

  not_before()

    Return the time the certificate becomes valid, as seconds since epoch.

  not_after()

    Return the time the certificate expires, as seconds since epoch.

  allowed_usage(usage_list)

    Return True if the certificates Key Usage extension contains all constraints given in `usage_list`. Also return True if the certificate doesn’t have this extension. Example usage constraints are: `"DIGITAL_SIGNATURE"`, `"KEY_CERT_SIGN"`, `"CRL_SIGN"`.

  verify(intermediates=None, trusted=None, trusted_path=None, required_strength=0, hostname=None, reference_time=0 crls=None)

    Verify a certificate. Returns 0 if validation was successful, returns a positive error code if the validation was unsuccessful.

    `intermediates` is a list of untrusted subauthorities.

    `trusted` is a list of trusted root CAs.

    The trusted_path refers to a directory where one or more trusted CA certificates are stored.

    Set `required_strength` to indicate the minimum key and hash strength that is allowed. For instance setting to 80 allows 1024-bit RSA and SHA-1. Setting to 110 requires 2048-bit RSA and SHA-256 or higher. Set to zero to accept a default.

    If `hostname` is given, it will be checked against the certificates CN field.

    Set `reference_time` to be the time which the certificate chain is validated against. Use zero (default) to use the current system clock.

    `crls` is a list of CRLs issued by either trusted or untrusted authorities.

  classmethod validation_status(error_code)

    Return an informative string associated with the verification return code.

  is_revoked(self, crl)

    Check if the certificate (`self`) is revoked on the given `crl`.

## X509CRL

class botan3.X509CRL(filename=None, buf=None)

  Class representing an X.509 Certificate Revocation List.

  A CRL in PEM or DER format can be loaded from a file, with the `filename` argument, or from a bytestring, with the `buf` argument.