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SHA-1

SHA-1 produces the 160 bit digest of a message. For example:

>>> from Crypto.Hash import SHA1
>>>
>>> h = SHA1.new()
>>> h.update(b'Hello')
>>> print h.hexdigest()

SHA stands for Secure Hash Algorithm.

Warning

This algorithm is not considered secure. Do not use it for new designs.

Warning

SHA-1 is vulnerable to length-extension attacks, which are relevant if you are computing the hash of a secret message.

For instance, let's say you were planning to build a cheap MAC by concatenating a secret key to a public message m (bad idea!):

h = \text{SHA-1}(m || k)

By only knowing the digest h and the length of m and k, the attacker can easily compute a second digest h':

h' = \text{SHA-1}(m || p || z)

where p is a well-known bit string and the attacker can pick a bit string z at will.

.. py:function:: Crypto.SHA1.new(msg=None)

    Create a new hash object.

    :param msg:
        Optional. The very first chunk of the message to hash.
        It is equivalent to an early call to :func:`update`.
    :type msg: byte string

    :returns: A :class:`SHA1_Hash` hash object


.. py:class:: Crypto.SHA1.SHA1_Hash

    A SHA-1 hash object.
    Do not instantiate directly.
    Use the :func:`new` function.

    :ivar oid: ASN.1 Object ID
    :vartype oid: string

    :ivar block_size: the size in bytes of the internal message block,
                      input to the compression function
    :vartype block_size: integer

    :ivar digest_size: the size in bytes of the resulting hash
    :vartype digest_size: integer

    .. py:method:: update(msg)

        Continue hashing of a message by consuming the next chunk of data.

        :param msg: The next chunk of the message being hashed.
        :type param: byte string

    .. py:method:: digest()

        Return the **binary** (non-printable) digest of the message that has been hashed so far.

        :return: The hash digest, computed over the data processed so far.
                 Binary form.
        :rtype: byte string

    .. py:method:: hexdigest()

        Return the **printable** digest of the message that has been hashed so far.

        :return: The hash digest, computed over the data processed so far.
                 Hexadecimal encoded.
        :rtype: string