make a new vocabulary for safe primes

basis/math/primes/safe/authors.txt

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+Doug Coleman

basis/math/primes/safe/safe-docs.factor

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+! Copyright (C) 2009 Doug Coleman.
+! See http://factorcode.org/license.txt for BSD license.
+USING: combinators.short-circuit help.markup help.syntax kernel
+math math.functions math.primes random ;
+IN: math.primes.safe
+
+HELP: next-safe-prime
+{ $values
+    { "n" integer }
+    { "q" integer }
+}
+{ $description "Tests consecutive numbers and returns the next safe prime. A safe prime is desirable in cryptography applications such as Diffie-Hellman and SRP6." } ;
+
+HELP: random-safe-prime
+{ $values
+    { "numbits" integer }
+    { "p" integer }
+}
+{ $description "Returns a safe prime number " { $snippet "numbits" } " bits in length, with the topmost bit set to one." } ;
+
+HELP: safe-prime?
+{ $values
+    { "q" integer }
+    { "?" "a boolean" }
+}
+{ $description "Tests whether the number is a safe prime. A safe prime " { $snippet "p" } " must be prime, as must " { $snippet "(p - 1) / 2" } "." } ;
+
+
+ARTICLE: "math.primes.safe" "Safe prime numbers"
+"The " { $vocab-link "math.primes.safe" } " vocabulary implements words to calculate safe prime numbers. Safe primes are of the form p = 2q + 1, where p,q are prime. Safe primes have desirable qualities for cryptographic applications." $nl
+
+"Testing if a number is a safe prime:"
+{ $subsection safe-prime? }
+"Generating safe prime numbers:"
+{ $subsection next-safe-prime }
+{ $subsection random-safe-prime } ;
+
+ABOUT: "math.primes.safe"

basis/math/primes/safe/safe-tests.factor

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+! Copyright (C) 2009 Doug Coleman.
+! See http://factorcode.org/license.txt for BSD license.
+USING: math.primes.safe math.primes.safe.private tools.test ;
+IN: math.primes.safe.tests
+
+[ 863 ] [ 862 next-safe-prime ] unit-test
+[ f ] [ 862 safe-prime? ] unit-test
+[ t ] [ 7 safe-prime? ] unit-test
+[ f ] [ 31 safe-prime? ] unit-test
+[ t ] [ 47 safe-prime-candidate? ] unit-test
+[ t ] [ 47 safe-prime? ] unit-test
+[ t ] [ 863 safe-prime? ] unit-test
+
+[ 47 ] [ 31 next-safe-prime ] unit-test

basis/math/primes/safe/safe.factor

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+! Copyright (C) 2009 Doug Coleman.
+! See http://factorcode.org/license.txt for BSD license.
+USING: combinators.short-circuit kernel math math.functions
+math.primes random ;
+IN: math.primes.safe
+
+<PRIVATE
+
+: safe-prime-candidate? ( n -- ? )
+    1 + 6 divisor? ;
+
+: next-safe-prime-candidate ( n -- candidate )
+    next-prime dup safe-prime-candidate?
+    [ next-safe-prime-candidate ] unless ;
+
+PRIVATE>
+
+: safe-prime? ( q -- ? )
+    {
+        [ 1 - 2 / dup integer? [ prime? ] [ drop f ] if ]
+        [ prime? ]
+    } 1&& ;
+
+: next-safe-prime ( n -- q )
+    next-safe-prime-candidate
+    dup safe-prime? [ next-safe-prime ] unless ;
+
+: random-safe-prime ( numbits -- p )
+    random-bits* next-safe-prime ;