Encryption doesn't translate to the ability to prove a message senders identity.
The two factors authenticity and non repudiation are insured by the use of hash functions in digital
signatures
a hash function is a one way function.
You have to find a hash a characteristic fixed length trade of a variable length message
cryptographic hash functions should also guarantee you the maximum possible randomness of the result.
Minimize the risk that the hatch result generated from two different inputs will be the same and make
a hash result from two very similar sets of data dissimilar as possible.
This means that for any text computing the hash should be easy fast efficient and not complex.
While mapping a text to a signature should be very hard to achieve.
Different inputs should also be mapped to different hashes.
The use of hash functions is connected with a serious threat.
The security of symmetric or asymmetric algorithms varies.
You can be certain that the hash functions used today are not secure.
What's the reason for the state.
The first problem that pertains to hash functions is the birthday paradox and the attack that exploits
it.
What is this problem about.
If you get together with a group of 23 people what is the probability that two of the people have the
same birthday.
As it turns out this probability is surprisingly high it's over 50 percent.
There are 365 days in a year.
So 23 people would be enough for the probability of discovering that at least one pair and the group
share the same birthday over 50 percent if seven more people made up.
The group will increase to 30.
The probability of at least two people in the group having the same birthday increases to over 70 percent.
Why is the probability so high.
First since there are 365 days in a year the first collision or match will occur after a give or take
the 19th attempt 19 a square root of 365 in statistics a first match will occur likely soon after the
square root of all possibilities.
In a group of pointone you can create n times and minus one divided by two to one hundred ninety pairs
for each of the pairs.
The probability of having the same birthday is 1 to 365.
You see the data to calculate the probability computing 20 times 20 minus one divided by two times divided
by 365 gives us 380 730 slightly over 50 percent.
Why even mention this
from the birthday paradox you know that the risk of college in structure is quite a bit.
It's certainly bigger than it would seem.
How can you protect yourself against this problem.
How is this shortcoming addressed.
There's one viable solution used hash function results have to be lengthened.
We started with the 128 bit length.
Now there are even hash function results that are 512 bits long what hash functions are there.
The first function is the MDI family message digest
these hash functions were developed by Ron Rivest M.D. 2 was published in 1989 and before in 1990 and
the five in 1991 the function's return 128 bit long outputs for several years now it's been known that
there are a phishing attacks on all versions of the M.D hash function.
For this reason the functions are not considered secure and are not recommended MT 5 is still widely
used though.
For example in Internet Applications
an other option is using the SAHD family of hash functions.
They were developed by the NSA.
The hash that's returned is quite longer at 160 bits.
The first of the S.H. a hash functions as actuates 0 and SH 1 are not secure censor publication they've
been shown to be susceptible to attacks.
The security of the former is 39 bits.
All the security of the latter is 63 bits.
There's also another variation of the hash function to OSHA to create hashes that are 256 or 512 bits
in length.
While some Chinese researchers have announced that they have successfully cracked sh to.
There's no official proof to support this claim.