Signing Interface — It's Dangerous documentation

Signing Interface

The most basic interface is the signing interface. The Signer class can be used to attach a signature to a specific string:

from itsdangerous import Signer
s = Signer("secret-key")
s.sign("my string")
b'my string.wh6tMHxLgJqB6oY1uT73iMlyrOA'

The signature is appended to the string, separated by a dot. To validate the string, use the unsign() method:

s.unsign(b"my string.wh6tMHxLgJqB6oY1uT73iMlyrOA")
b'my string'

If unicode strings are provided, an implicit encoding to UTF-8 happens. However after unsigning you won’t be able to tell if it was unicode or a bytestring.

If the value is changed, the signature will no longer match, and unsigning will raise a BadSignature exception:

s.unsign(b"different string.wh6tMHxLgJqB6oY1uT73iMlyrOA")
Traceback (most recent call last):
  ...
itsdangerous.exc.BadSignature: Signature "wh6tMHxLgJqB6oY1uT73iMlyrOA" does not match

To record and validate the age of a signature, see Signing With Timestamps.