Understanding Symmetric Cryptography NEO GUI Wallet .pdf
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Understanding Symmetric Cryptography
Symmetric cryptography, also known as secret key (as opposed to public key cryptography), is the oldest
form of encryption. It has traces of its use by the Egyptians around 2000 BC.
A good way to learn more about this with is the Neon GUI Wallet.
One of the basic concepts of cryptography is the symmetric key, which is information designed to
encrypt and decrypt a message, which may be based on the security of any communication. An
algorithm ROT13 as such has no key, just to know that this method was used to encrypt a message and
can be accessed in clear text. You can change the ROT13 by changing the offset value, that value
becomes the key. All possible keys then offer 26 possible discrepancies. Although a little more tedious
decryption remains accessible even by hand. And with computers, it can test billions and billions of keys
We see emerging from this example the importance of keys and restrictions. Auguste Kerckhoffs (The
military cryptographer, 1883) is certainly one of the first to have fully understood this: be sure to expect,
the algorithm must be disclosed. This is now known as Kerckhoffs principle. We must add that this key
can take sufficient values for a comprehensive attack - systematic tests of all the keys - can be carried
out. We are talking about security complexity.
This security complexity is obviously dependent on time, the performance of computing resources, an
encryption system is always facing new challenges. The illustration of this problem is the DES, this
system has become obsolete because it cannot produce enough keys. It is believed that, currently, 280
is the bare minimum level of security. As an indication, the latest standard chosen by America in
December 2001, AES uses keys whose size is at least 128 bits of which there are 2128 in total. To give an
order of magnitude to these, it is about 3.4 in 1038 possible keys, the age of the universe is 1010 years,
if we suppose it is possible to test 1 000 billion keys per second it will take more than a billion times the
age of the universe. In such cases it is reasonable to assume that our algorithm is safe. However, it is a
very strong case on the algorithm to assume that the only way to break it is to conduct a comprehensive
attack: there are many loopholes that can reveal an algorithm.
The question posed by this notion of security is the complexity of absolute theory. The drawback is that
to encrypt a message of n bits, we must first have exchanged a key n bit with the recipient of the
message, and this way is not safe. Very few cases require such a system, however it was the system used
for the Hotline between the Kremlin and the White House.