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Apply nonce bit-length mitigation to stop timing leakage. #14

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Apply nonce bit-length mitigation to stop timing leakage. #14

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11 changes: 9 additions & 2 deletions lib/ecdsa/sign.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -25,10 +25,17 @@ def self.sign(group, private_key, digest, temporary_key)

# Second part of step 1: Select ephemeral elliptic curve key pair
# temporary_key was already selected for us by the caller
r_point = group.new_point temporary_key
point_field = PrimeField.new(group.order)
k = point_field.mod(temporary_key)
ks = k + group.order
kt = ks + group.order
if ECDSA.bit_length(ks) == ECDSA.bit_length(group.order)
r_point = group.new_point kt
else
r_point = group.new_point ks

# Steps 2 and 3
point_field = PrimeField.new(group.order)

r = point_field.mod(r_point.x)
return nil if r.zero?

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