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.. _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).
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