Ed25519ScalarOps

net.i2p.crypto.eddsa.math.ed25519.Ed25519ScalarOps

public class Ed25519ScalarOpsextends Object implements ScalarOps

Class for reducing a huge integer modulo the group order q and doing a combined multiply plus add plus reduce operation.

$q = 2^{252} + 27742317777372353535851937790883648493$.

See Also:

Constructor Details
- Ed25519ScalarOps
  public Ed25519ScalarOps()
  Constructor. The reduction and fused multiply-add are pure arithmetic over their arguments, so an instance carries no state.
Method Details
- reduce
  public byte[] reduce(byte[] s)
  Reduction modulo the group order $q$.
  Input: $s[0]+256*s[1]+\dots+256^{63}*s[63] = s$
  Output: $s[0]+256*s[1]+\dots+256^{31}*s[31] = s \bmod q$ where $q = 2^{252} + 27742317777372353535851937790883648493$.
  Specified by:
  reduce in interface ScalarOps
  Parameters:
  s - the scalar to reduce
  Returns:
  $s \bmod l$
- multiplyAndAdd
  public byte[] multiplyAndAdd(byte[] a, byte[] b, byte[] c)
  $(ab+c) \bmod q$
  Input:
  $a[0]+256*a[1]+\dots+256^{31}*a[31] = a$
  $b[0]+256*b[1]+\dots+256^{31}*b[31] = b$
  $c[0]+256*c[1]+\dots+256^{31}*c[31] = c$
  Output: $result[0]+256*result[1]+\dots+256^{31}*result[31] = (ab+c) \bmod q$ where $q = 2^{252} + 27742317777372353535851937790883648493$.
  See the comments in reduce(byte[]) for an explanation of the algorithm.
  Specified by:
  multiplyAndAdd in interface ScalarOps
  Parameters:
  a - the first multiplicand, a scalar in little-endian form
  b - the second multiplicand, a scalar in little-endian form
  c - the addend, a scalar in little-endian form
  Returns:
  $(a*b + c) \bmod l$

Constructor Summary