diff options
Diffstat (limited to 'bcprov/src/main/java/org/bouncycastle/math/ec/Tnaf.java')
| -rw-r--r-- | bcprov/src/main/java/org/bouncycastle/math/ec/Tnaf.java | 49 |
1 files changed, 20 insertions, 29 deletions
diff --git a/bcprov/src/main/java/org/bouncycastle/math/ec/Tnaf.java b/bcprov/src/main/java/org/bouncycastle/math/ec/Tnaf.java index 42d6738..236bbc8 100644 --- a/bcprov/src/main/java/org/bouncycastle/math/ec/Tnaf.java +++ b/bcprov/src/main/java/org/bouncycastle/math/ec/Tnaf.java @@ -535,45 +535,36 @@ class Tnaf int m = curve.getM(); int a = curve.getA().toBigInteger().intValue(); byte mu = curve.getMu(); - int h = curve.getH().intValue(); + int shifts = getShiftsForCofactor(curve.getCofactor()); int index = m + 3 - a; BigInteger[] ui = getLucas(mu, index, false); - - BigInteger dividend0; - BigInteger dividend1; if (mu == 1) { - dividend0 = ECConstants.ONE.subtract(ui[1]); - dividend1 = ECConstants.ONE.subtract(ui[0]); - } - else if (mu == -1) - { - dividend0 = ECConstants.ONE.add(ui[1]); - dividend1 = ECConstants.ONE.add(ui[0]); - } - else - { - throw new IllegalArgumentException("mu must be 1 or -1"); + ui[0] = ui[0].negate(); + ui[1] = ui[1].negate(); } - BigInteger[] si = new BigInteger[2]; + BigInteger dividend0 = ECConstants.ONE.add(ui[1]).shiftRight(shifts); + BigInteger dividend1 = ECConstants.ONE.add(ui[0]).shiftRight(shifts).negate(); - if (h == 2) - { - si[0] = dividend0.shiftRight(1); - si[1] = dividend1.shiftRight(1).negate(); - } - else if (h == 4) - { - si[0] = dividend0.shiftRight(2); - si[1] = dividend1.shiftRight(2).negate(); - } - else + return new BigInteger[] { dividend0, dividend1 }; + } + + protected static int getShiftsForCofactor(BigInteger h) + { + if (h != null) { - throw new IllegalArgumentException("h (Cofactor) must be 2 or 4"); + if (h.equals(ECConstants.TWO)) + { + return 1; + } + if (h.equals(ECConstants.FOUR)) + { + return 2; + } } - return si; + throw new IllegalArgumentException("h (Cofactor) must be 2 or 4"); } /** |