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+Cryptosuite - A cryptographic library for Arduino
+Copyright (C) 2010 Peter Knight (Cathedrow)
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+
+SHA implements secure hash functions that can be used for cryptography, data integrity and security purposes.
+
+Sha covers the following standards:
+ SHA-1 (FIPS 180-2)
+ SHA-256 (FIPS 180-2)
+ HMAC-SHA-1 (FIPS 198a)
+ HMAC-SHA-256 (FIPS 198a)
+
+What is a hash function?
+ A hash function takes a message, and generates a number.
+ A good hash function has the following properties:
+ The number is large enough that you will never find two messages with the same number (a 'collision')
+ It is computationally unfeasible to extract message information from its hash (without trying every possible combination)
+ A small (1 bit) change in the message will produce a huge (approximately half of all bits) change in the hash.
+ Fast to calculate
+
+ SHA is slower than simple hashes (eg. parity), but has very high security - high enough to be used in currency transactions and confidential documents.
+ SHA-1 is currently secure, but there is some suggestion it may not be for much longer.
+ SHA-256 is slightly slower, but has higher security.
+
+What is an HMAC?
+ HMACs are Hashed Message Authentication Codes. Using them, it is possible to prove that you have a secret key without actually disclosing it.