PyOTP - The Python One-Time Password Library¶
PyOTP is a Python library for generating and verifying one-time passwords. It can be used to implement two-factor (2FA) or multi-factor (MFA) authentication methods in web applications and in other systems that require users to log in.
Open MFA standards are defined in RFC 4226 (HOTP: An HMAC-Based One-Time Password Algorithm) and in RFC 6238 (TOTP: Time-Based One-Time Password Algorithm). PyOTP implements server-side support for both of these standards. Client-side support can be enabled by sending authentication codes to users over SMS or email (HOTP) or, for TOTP, by instructing users to use Google Authenticator, Authy, or another compatible app. Users can set up auth tokens in their apps easily by using their phone camera to scan otpauth:// QR codes provided by PyOTP.
Implementers should read and follow the HOTP security requirements and TOTP security considerations sections of the relevant RFCs. At minimum, application implementers should follow this checklist:
Ensure transport confidentiality by using HTTPS
Ensure HOTP/TOTP secret confidentiality by storing secrets in a controlled access database
Deny replay attacks by rejecting one-time passwords that have been used by the client (this requires storing the most recently authenticated timestamp, OTP, or hash of the OTP in your database, and rejecting the OTP when a match is seen)
Throttle brute-force attacks against your application’s login functionality
When implementing a “greenfield” application, consider supporting FIDO U2F/WebAuthn in addition to HOTP/TOTP. U2F uses asymmetric cryptography to avoid using a shared secret design, which strengthens your MFA solution against server-side attacks. Hardware U2F also sequesters the client secret in a dedicated single-purpose device, which strengthens your clients against client-side attacks. And by automating scoping of credentials to relying party IDs (application origin/domain names), U2F adds protection against phishing attacks. One implementation of FIDO U2F/WebAuthn is PyOTP’s sister project, PyWARP.
We also recommend that implementers read the OWASP Authentication Cheat Sheet and NIST SP 800-63-3: Digital Authentication Guideline for a high level overview of authentication best practices.
Quick overview of using One Time Passwords on your phone¶
OTPs involve a shared secret, stored both on the phone and the server
OTPs can be generated on a phone without internet connectivity
OTPs should always be used as a second factor of authentication (if your phone is lost, you account is still secured with a password)
Google Authenticator and other OTP client apps allow you to store multiple OTP secrets and provision those using a QR Code
Installation¶
pip install pyotp
Usage¶
Time-based OTPs¶
totp = pyotp.TOTP('base32secret3232')
totp.now() # => '492039'
# OTP verified for current time
totp.verify('492039') # => True
time.sleep(30)
totp.verify('492039') # => False
Counter-based OTPs¶
hotp = pyotp.HOTP('base32secret3232')
hotp.at(0) # => '260182'
hotp.at(1) # => '055283'
hotp.at(1401) # => '316439'
# OTP verified with a counter
hotp.verify('316439', 1401) # => True
hotp.verify('316439', 1402) # => False
Generating a Secret Key¶
A helper function is provided to generate a 16 character base32 secret, compatible with Google Authenticator and other OTP apps:
pyotp.random_base32()
Some applications want the secret key to be formatted as a hex-encoded string:
pyotp.random_hex() # returns a 32-character hex-encoded secret
Google Authenticator Compatible¶
PyOTP works with the Google Authenticator iPhone and Android app, as well as other OTP apps like Authy. PyOTP includes the ability to generate provisioning URIs for use with the QR Code scanner built into these MFA client apps:
pyotp.totp.TOTP('JBSWY3DPEHPK3PXP').provisioning_uri(name='alice@google.com', issuer_name='Secure App')
>>> 'otpauth://totp/Secure%20App:alice%40google.com?secret=JBSWY3DPEHPK3PXP&issuer=Secure%20App'
pyotp.hotp.HOTP('JBSWY3DPEHPK3PXP').provisioning_uri(name="alice@google.com", issuer_name="Secure App", initial_count=0)
>>> 'otpauth://hotp/Secure%20App:alice%40google.com?secret=JBSWY3DPEHPK3PXP&issuer=Secure%20App&counter=0'
This URL can then be rendered as a QR Code (for example, using https://github.com/neocotic/qrious) which can then be scanned and added to the users list of OTP credentials.
Parsing these URLs is also supported:
pyotp.parse_uri('otpauth://totp/Secure%20App:alice%40google.com?secret=JBSWY3DPEHPK3PXP&issuer=Secure%20App')
>>> <pyotp.totp.TOTP object at 0xFFFFFFFF>
pyotp.parse_uri('otpauth://hotp/Secure%20App:alice%40google.com?secret=JBSWY3DPEHPK3PXP&issuer=Secure%20App&counter=0'
>>> <pyotp.totp.HOTP object at 0xFFFFFFFF>
Working example¶
Scan the following barcode with your phone’s OTP app (e.g. Google Authenticator):
Now run the following and compare the output:
import pyotp
totp = pyotp.TOTP("JBSWY3DPEHPK3PXP")
print("Current OTP:", totp.now())
API documentation¶
-
pyotp.parse_uri(uri: str) → pyotp.otp.OTP[source]¶ Parses the provisioning URI for the OTP; works for either TOTP or HOTP.
- Parameters
uri – the hotp/totp URI to parse
- Returns
OTP object
-
class
pyotp.totp.TOTP(s: str, digits: int = 6, digest: Any = <built-in function openssl_sha1>, name: Optional[str] = None, issuer: Optional[str] = None, interval: int = 30)[source]¶ Handler for time-based OTP counters.
-
at(for_time: Union[int, datetime.datetime], counter_offset: int = 0) → str[source]¶ Accepts either a Unix timestamp integer or a datetime object.
To get the time until the next timecode change (seconds until the current OTP expires), use this instead:
totp = pyotp.TOTP(...) time_remaining = totp.interval - datetime.datetime.now().timestamp() % totp.interval
- Parameters
for_time – the time to generate an OTP for
counter_offset – the amount of ticks to add to the time counter
- Returns
OTP value
-
provisioning_uri(name: Optional[str] = None, issuer_name: Optional[str] = None, image: Optional[str] = None) → str[source]¶ Returns the provisioning URI for the OTP. This can then be encoded in a QR Code and used to provision an OTP app like Google Authenticator.
-
timecode(for_time: datetime.datetime) → int[source]¶ Accepts either a timezone naive (for_time.tzinfo is None) or a timezone aware datetime as argument and returns the corresponding counter value (timecode).
-
verify(otp: str, for_time: Optional[datetime.datetime] = None, valid_window: int = 0) → bool[source]¶ Verifies the OTP passed in against the current time OTP.
- Parameters
otp – the OTP to check against
for_time – Time to check OTP at (defaults to now)
valid_window – extends the validity to this many counter ticks before and after the current one
- Returns
True if verification succeeded, False otherwise
-
-
class
pyotp.hotp.HOTP(s: str, digits: int = 6, digest: Any = <built-in function openssl_sha1>, name: Optional[str] = None, issuer: Optional[str] = None, initial_count: int = 0)[source]¶ Handler for HMAC-based OTP counters.
-
at(count: int) → str[source]¶ Generates the OTP for the given count.
- Parameters
count – the OTP HMAC counter
- Returns
OTP
-
provisioning_uri(name: Optional[str] = None, initial_count: Optional[int] = None, issuer_name: Optional[str] = None, image: Optional[str] = None) → str[source]¶ Returns the provisioning URI for the OTP. This can then be encoded in a QR Code and used to provision an OTP app like Google Authenticator.
- Parameters
name – name of the user account
initial_count – starting HMAC counter value, defaults to 0
issuer_name – the name of the OTP issuer; this will be the organization title of the OTP entry in Authenticator
- Returns
provisioning URI
-
-
pyotp.utils.build_uri(secret: str, name: str, initial_count: Optional[int] = None, issuer: Optional[str] = None, algorithm: Optional[str] = None, digits: Optional[int] = None, period: Optional[int] = None, image: Optional[str] = None) → str[source]¶ Returns the provisioning URI for the OTP; works for either TOTP or HOTP.
This can then be encoded in a QR Code and used to provision the Google Authenticator app.
For module-internal use.
- Parameters
secret – the hotp/totp secret used to generate the URI
name – name of the account
initial_count – starting counter value, defaults to None. If none, the OTP type will be assumed as TOTP.
issuer – the name of the OTP issuer; this will be the organization title of the OTP entry in Authenticator
algorithm – the algorithm used in the OTP generation.
digits – the length of the OTP generated code.
period – the number of seconds the OTP generator is set to expire every code.
image – optional logo image url
- Returns
provisioning uri
-
pyotp.utils.strings_equal(s1: str, s2: str) → bool[source]¶ Timing-attack resistant string comparison.
Normal comparison using == will short-circuit on the first mismatching character. This avoids that by scanning the whole string, though we still reveal to a timing attack whether the strings are the same length.