GENERALITIES

	A. MD5 - generalities
	
	1. MD5 is a block hash function, the size of the block is 512 bits
	2. the input for MD5 is a message (file) of arbitrary length
	3. the output is a fixed length (128 bits) message digest
	4. specified by RFC 1321, april 1992
	5. MD5 was developed by Rivest in 1991
	6. MD5 collisions have been found recently, for example a single block (2 padded messages of 512 bits) collision was found in 2012 by Marc Stevens 

	B. SHA-1 - generalities

	1. SHA-1 is a block hash function, the size of the block is 512 bits
	2. the input for SHA-1 is a message (file) of arbitrary length
	3. the output is a fixed length (160 bits) message digest
	4. fips 180-1, april 1995
	5. SHA-1 was designed by the National Institute of Standards and Technology (NIST) 
	   and the National Security Agency (NSA) for use with the Digital Signature Standard 
	6. a collision was found in feb. 2017 by CWI and Google (two different pdf files with the same SHA-1 digest)

	C. DES - generalities

	1. DES is a symmetric (private key) encryption algorithm, of type block, and uses a 56+8 bits key
	2. the input for DES is a message (file) of arbitrary length
	3. the output is the encrypted message
	4. specified by fips 46-1, 46-2, 46-3
	5. DES was adopted as standard in jan. 1977 (fips 46-1). the last version is fips 46-3 (1998)
	   and contains the specification for both DES and T(riple)-DES.
	6. considered to be unsafe, due to the short size key. replaced by T-DES si AES.

	D. AES - generalities

	1. AES is a symmetric (private key) encryption algorithm, of type block (the size of the block is 128 bits)
	   and uses keys of size 128, 192 and 256 bits
	2. the input pentru AES is an arbitrary size message
	3. the output is the encrypted message
	4. specified by fips 197, nov 2001
	5. AES was adopted as a standard in nov. 2001 (fips 197). it became mandatory for the federal
	   agecies of the USA in may 2002. the algorithm used by this standard was created by V. Rijmen and J. Daemen.   
	6. deemed to be safe for the foreseeable future.