# Python Binding

New 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.

Starting in 2.8, the class names were renamed to match Python standard conventions. However aliases are defined which allow older code to continue to work; the older names are mentioned as “previously X”. These aliases will be removed in a future major release.

## Versioning

`botan.``version_major`()

  Returns the major number of the library version.

`botan.``version_minor`()

  Returns the minor number of the library version.

`botan.``version_patch`()

  Returns the patch number of the library version.

`botan.``version_string`()

  Returns a free form version string for the library

## Random Number Generators

class `botan.``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).

  `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 `botan.``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 `botan.``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 `botan.``SymmetricCipher`(object, algo, encrypt = True)

  > Previously `cipher`

  > The algorithm is spcified 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

`botan.``bcrypt`(passwd, rng, work_factor = 10)

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

`botan.``check_bcrypt`(passwd, bcrypt)

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

## PBKDF

`botan.``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

`botan.``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

New in version 2.8.0.

`botan.``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

`botan.``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 `botan.``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.

  `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)`

  `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")`.

  `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 `botan.``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 group “curve25519” (which is actually a completely distinct key type with a non-standard encoding).

  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

  `get_public_key`()

    Return a public_key object

  `to_pem`()

    Return the PEM encoded private key (unencrypted)

  `to_der`()

    Return the PEM encoded private key (unencrypted)

  `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.

  `to_der`()

    Like `self.export(False)`

  `to_pem`()

    Like `self.export(True)`

  `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.

## Public Key Operations

class `botan.``PKEncrypt`(pubkey, padding)

  Previously `pk_op_encrypt`

  `encrypt`(msg, rng)

class `botan.``PKDecrypt`(privkey, padding)

  Previously `pk_op_decrypt`

  `decrypt`(msg)

class `botan.``PKSign`(privkey, hash_w_padding)

  Previously `pk_op_sign`

  `update`(msg)
  `finish`(rng)

class `botan.``PKVerify`(pubkey, hash_w_padding)

  Previously `pk_op_verify`

  `update`(msg)
  `check_signature`(signature)

class `botan.``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.

## Multiple Precision Integers (MPI)

New in version 2.8.0.

class `botan.``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`

## Format Preserving Encryption (FE1 scheme)

New in version 2.8.0.

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

  Initialize an instance for format preserving encryption

  `encrypt`(msg, tweak)

    The msg should be a botan2.MPI or an object which can be converted to one

  `decrypt`(msg, tweak)

    The msg should be a botan2.MPI or an object which can be converted to one

## HOTP

New in version 2.8.0.

class `botan.``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 `botan.``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 unsuccesful.

    `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 `botan.``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.