Encrypted Password

Crypt algorithm:
In[]:=
crypt[password_]:=With[{enc=Encrypt[password,ByteArray[{0,0,0,0,0,0,0,0}],Method-><|"InitializationVector"->ByteArray[{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}]|>]},BaseEncode[enc["Data"]]];
In[]:=
passwdfile=<||>;
To add a new user:
In[]:=
SignUp[user_,password_]:=AssociateTo[passwdfile,user->crypt[password]];
In[]:=
SignUp["alice","my_pass"];​​passwdfile
Out[]=
alicey4gsO7/JshJC23bqGnXlvg==
In[]:=
SignUp["bob","next_pass"];​​passwdfile
Out[]=
alicey4gsO7/JshJC23bqGnXlvg==,bobcCsp3junfaqBvMkZoQHU9Q==
To log in, the system takes the password that you typed, uses it to encrypt a block of 0 bytes, and compares if it matches the value stored in the /etc/passwd file:
In[]:=
LogIn[user_,password_]:=​​If[passwdfile[user]===crypt[password],(*storedin/etc/passwdfile=encryptedblock*)​​"Login as "<>user<>" successful!",​​"Login failed."];
In[]:=
LogIn["alice","12345678"]
Out[]=
Login failed.
In[]:=
LogIn["alice","my_pass"]
Out[]=
Login as alice successful!

Rainbow Table Attack

Common passwords:
123456
O2lURwjNgQjBwIVsL1D/uQ
12345678
FjIolUT/tpP47leYswBl9w
password
rzbhDUtxz53ChwzA2C+eZg
password1
cmBkNwQSH2z5QbcPEYEBuQ
11111
RklJD+e/T2v3XEqUwtUyTw
qwerty
gaoeHZm7d9KTeLfOq3kljw
123321
/46FF5WIAbZC9ZUNy+isDg
...
...

Hash Functions

In[]:=
book=ExampleData[{"Text","AliceInWonderland"}];​​Snippet[book,3]
Out[]=
I--DOWN THE RABBIT-HOLE Alice was beginning to get very tired of sitting by hersister on the bank, and of having nothing to do. Once or twice she had peepedinto the book her sister was reading, but it had no pictures or conversations in
In[]:=
StringLength[book]
Out[]=
51722
In[]:=
Hash[book,"SHA","HexString"]
Out[]=
e34ff81046172fd124023ebcd8d34af0a1ce62fa
A digest is also very compact:
ByteCount[book]
ByteCount[Hash[book]]

Caesar Cipher

In[]:=
key=2
In[]:=
letters=CharacterRange["a","z"]
In[]:=
shiftedLetters=Join[letters[[key+1;;]],letters[[;;key]]]
In[]:=
Grid[{letters,shiftedLetters},Frame->All]
encryptWithShiftedLetters=Thread[letters->shiftedLetters]
decryptFromShifterdLetters=Thread[shiftedLetters->letters]
StringReplace["test",encryptWithShiftedLetters]
StringReplace[" ",decryptFromShifterdLetters]

Break the Caesar Cipher

In[]:=
ResourceFunction["CrackCaesarCipher"]["Qeb nrfzh yoltk clu grjmp lsbo qeb ixwv ald"]

Symmetric Key Cryptography

In[]:=
key=GenerateSymmetricKey[Method->"AES256"]
Out[]=
SymmetricKey
Cipher: AES256
Key size:
256
b

In[]:=
encryptedMessage=Encrypt[key,"Dear Bob, I hope this message finds you well..."]
Out[]=
EncryptedObject
Data length:
48
B
Original form: String

In[]:=
BaseEncode[encryptedMessage["Data"],"Base85ASCII"]
Out[]=
;KK;X'Nm+J<cA;>PLb/,/Eu9T/p\5tZQmui5MPOGV@c*Qpl.Qt-D1P>4$T?H
In[]:=
Decrypt[key,encryptedMessage]
Out[]=
Dear Bob, I hope this message finds you well...

Asymmetric Key Cryptography

In[]:=
keysAbrita=GenerateAsymmetricKeyPair[]
Out[]=
PrivateKeyPrivateKey
Type: RSA
Public modulus size:
2048
b
Private exponent size:
2040
b
,PublicKeyPublicKey
Type: RSA
Public modulus size:
2048
b

In[]:=
sharePublicKey=keysAbrita["PublicKey"]
Out[]=
PublicKey
Type: RSA
Public modulus size:
2048
b

In[]:=
hidePrivateKey=keysAbrita["PrivateKey"]
Out[]=
PrivateKey
Type: RSA
Public modulus size:
2048
b
Private exponent size:
2040
b

In[]:=
message=Encrypt[sharePublicKey,"Good luck for the exam"]
Out[]=
EncryptedObject
Data length:
256
B
Original form: String

In[]:=
BaseEncode[message["Data"],"Base85ASCII"]
Out[]=
*F/LKK]Ga5Y63K6h7)&=%ec8pQ\Z\O5j&R<ie(Tt[2!Z!dZ;?KO2K@>]MFZ`p8R,`H;@Y(7_Ffq@E,"+j:mV5">4Q^9%3CtM[>cJHRh"5:(WRY94'/j'%R`#-RaJX.CTsDon4*M7H9?AVn3s<@!2P:!15.!GnL]ZF!X'.,kmac^PC'$Jb`ad]KaZT@H^f\5K$=oiWKQiU*`Cq84:S5K?RhP=G=P*Nug4=[@^u-0KuA;Q4rH<jPb(,!WiQ&YkF$M=>rE)U8UP+CID=Ir(D]I;ZIkedUfQ&=G6a0COY/5QorbKX\!\CA#KXM*-=WtY52'?
In[]:=
Decrypt[hidePrivateKey,message]
Out[]=
Good luck for the exam