Introduce lib/crapto and a frequency analysis service.

Signed-off-by: Philippe Pepos Petitclerc <ppeposp@gmail.com>

diff --git a/lib/crapto/crapto.nit b/lib/crapto/crapto.nit
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+++ b/lib/crapto/crapto.nit
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+# This file is part of NIT ( http://www.nitlanguage.org ).
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Cryptographic attacks and utilities.
+module crapto
+
+import english_utils

diff --git a/lib/crapto/english_utils.nit b/lib/crapto/english_utils.nit
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+# This file is part of NIT ( http://www.nitlanguage.org ).
+#
+# Copyright 2016 Philippe Pépos Petitclerc <ppeposp@gmail.com>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# English language utilities for cryptographic purposes.
+module english_utils
+
+redef class Sys
+       # English letter frequency map
+       var english_freqs: HashMap[Char, Float] is lazy do
+               var freqs = new HashMap[Char, Float]
+
+               freqs['a'] = 0.0651738
+               freqs['b'] = 0.0124248
+               freqs['c'] = 0.0217339
+               freqs['d'] = 0.0349835
+               freqs['e'] = 0.1041442
+               freqs['f'] = 0.0197881
+               freqs['g'] = 0.0158610
+               freqs['h'] = 0.0492888
+               freqs['i'] = 0.0558094
+               freqs['j'] = 0.0009033
+               freqs['k'] = 0.0050529
+               freqs['l'] = 0.0331490
+               freqs['m'] = 0.0202124
+               freqs['n'] = 0.0564513
+               freqs['o'] = 0.0596302
+               freqs['p'] = 0.0137645
+               freqs['q'] = 0.0008606
+               freqs['r'] = 0.0497563
+               freqs['s'] = 0.0515760
+               freqs['t'] = 0.0729357
+               freqs['u'] = 0.0225134
+               freqs['v'] = 0.0082903
+               freqs['w'] = 0.0171272
+               freqs['x'] = 0.0013692
+               freqs['y'] = 0.0145984
+               freqs['z'] = 0.0007836
+               freqs[' '] = 0.1918182
+
+               return freqs
+       end
+end
+
+redef class Text
+
+       # Score `self` according to english's letter frequency.
+       # This function is useful mainly for cryptography but could happen to be helpful
+       # elsewhere.
+       #
+       #     assert "aaaa".english_scoring > "bbbb".english_scoring
+       fun english_scoring: Float do
+
+               var freqs = english_freqs
+               var score = 0.0
+
+               for c in self do
+                       c = c.to_lower
+                       var points = freqs.get_or_null(c)
+                       if points != null then
+                               score += points
+                       end
+               end
+
+               return score
+
+       end
+end

diff --git a/lib/crapto/package.ini b/lib/crapto/package.ini
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+++ b/lib/crapto/package.ini
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+[package]
+name=crapto
+tags=crypto
+maintainer=Philippe Pépos Petitclerc <ppeposp@gmail.com>
+license=Apache-2.0
+[upstream]
+browse=https://github.com/nitlang/nit/tree/master/lib/crapto
+git=https://github.com/nitlang/nit.git
+git.directory=lib/crapto/
+homepage=http://nitlanguage.org
+issues=https://github.com/nitlang/nit/issues