.. _glossary:

Glossary
========

.. glossary::
   :sorted:

   ECC
     Elliptic Curve Cryptography, a term for all the different ways of using
     elliptic curves in cryptography. Also combined term for :term:`ECDSA`,
     :term:`EdDSA`, :term:`ECDH`.

   ECDSA
     Elliptic Curve Digital Signature Algorithm

   EdDSA
     Edwards curve based Digital Signature Algorithm, the alternative
     digital signature algorithm that's used for Curve25519 or Curve448

   ECDH
     Elliptic Curve Diffie-Hellman

   raw encoding
       Conversion of public, private keys and signatures (which in
       mathematical sense are integers or pairs of integers) to strings of
       bytes that does not use any special tags or encoding rules.
       For any given curve, all keys of the same type or signatures will be
       encoded to byte strings of the same length. In more formal sense,
       the integers are encoded as big-endian, constant length byte strings,
       where the string length is determined by the curve order (e.g.
       for NIST256p the order is 256 bits long, so the private key will be 32
       bytes long while public key will be 64 bytes long). The encoding of a
       single integer is zero-padded on the left if the numerical value is
       low. In case of public keys and signatures, which are comprised of two
       integers, the integers are simply concatenated.

   uncompressed
       The most common formatting specified in PKIX standards. Specified in
       X9.62 and SEC1 standards. The only difference between it and
       :term:`raw encoding` is the prepending of a 0x04 byte. Thus an
       uncompressed NIST256p public key encoding will be 65 bytes long.

   compressed
       The public point representation that uses half of bytes of the
       :term:`uncompressed` encoding (rounded up). It uses the first byte of
       the encoding to specify the sign of the y coordinate and encodes the
       x coordinate as-is. The first byte of the encoding is equal to
       0x02 or 0x03. Compressed encoding of NIST256p public key will be 33
       bytes long.

   hybrid
       A combination of :term:`uncompressed` and :term:`compressed` encodings.
       Both x and y coordinates are stored just as in :term:`compressed`
       encoding, but the first byte reflects the sign of the y coordinate. The
       first byte of the encoding will be equal to 0x06 or 0x7. Hybrid
       encoding of NIST256p public key will be 65 bytes long.

   PEM
       The acronym stands for Privacy Enhanced Mail, but currently it is used
       primarily as the way to encode :term:`DER` objects into text that can
       be either easily copy-pasted or transferred over email.
       It uses headers like ``-----BEGIN <type of contents>-----`` and footers
       like ``-----END <type of contents>-----`` to separate multiple
       types of objects in the same file or the object from the surrounding
       comments. The actual object stored is base64 encoded.

   DER
       Distinguished Encoding Rules, the way to encode :term:`ASN.1` objects
       deterministically and uniquely into byte strings.

   ASN.1
       Abstract Syntax Notation 1 is a standard description language for
       specifying serialisation and deserialisation of data structures in a
       portable and cross-platform way.

   bytes-like object
       All the types that implement the buffer protocol. That includes
       ``str`` (only on python2), ``bytes``, ``bytearray``, ``array.array``
       and ``memoryview`` of those objects.
       Please note that ``array.array`` serialisation (converting it to byte
       string) is endianess dependant! Signature computed over ``array.array``
       of integers on a big-endian system will not be verified on a
       little-endian system and vice-versa.

   set-like object
       All the types that support the ``in`` operator, like ``list``,
       ``tuple``, ``set``, ``frozenset``, etc.

   short Weierstrass curve
       A curve with the curve equation: :math:`x^2=y^3+ax+b`. Most popular
       curves use equation of this format (e.g. NIST256p).