Point Compression

In Elliptic Curve Cryptography (ECC), public keys are points on elliptic curves. An elliptic curve point is a point in a two-dimensional space.

Standards such as FIPS 186-2 (identical to ANSI X9.62) and IEEE 1363-2000 define the following three different representations (each in byte array format) of elliptic curve points:
  • Uncompressed
  • Hybrid
  • Compressed

The uncompressed point representation uses the usual ordered-pair representation specifying both x and y co-ordinates.

The hybrid point representation uses ordered-pair representation with an additional sign bit.

The compressed point representation requires only the x co-ordinate and a sign bit. Under this representation, the size of a public key is compressed to nearly half the size of the uncompressed representation, saving memory space and bandwidth.

Default Settings

Security Builder Crypto’s default behaviour is to express public keys using the compressed point representation whenever it outputs a public key value. Any of the three elliptic curve point representations are accepted for public key input.

Last modified: 2013-12-21

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