40 lines
868 B
Go
40 lines
868 B
Go
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package passwordvalidator
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import (
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"math"
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)
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// GetEntropy returns the entropy in bits for the given password
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// See the ReadMe for more information
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func GetEntropy(password string) float64 {
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return getEntropy(password)
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}
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func getEntropy(password string) float64 {
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base := getBase(password)
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length := getLength(password)
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// calculate log2(base^length)
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return logPow(float64(base), length, 2)
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}
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func logX(base, n float64) float64 {
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if base == 0 {
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return 0
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}
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// change of base formulae
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return math.Log2(n) / math.Log2(base)
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}
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// logPow calculates log_base(x^y)
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// without leaving logspace for each multiplication step
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// this makes it take less space in memory
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func logPow(expBase float64, pow int, logBase float64) float64 {
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// logb (MN) = logb M + logb N
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total := 0.0
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for i := 0; i < pow; i++ {
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total += logX(logBase, expBase)
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}
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return total
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}
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