I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that.
This's my method to encrypt :
I have a msg : "messages from father to his son" I have a key : "home" And the cipher text : "tsewmkwk fxse krhtjr mv lzl gvv"
I've created the Mathematics algorithm for the encryption, but get stuck for the decription. This's what I've made fro encryption :
msg : "messages from father to his son" key : "homemess ages fromfa th ert ohi"
So, I include the msg as part as the encryption method. And,
my problem is :
How is mathematical/cryptanalysis method for implement this procedure below ?
msg : "tsewmkwk fxse krhtjr mv lzl gvv" key : "homemess ages fromfa th ert ohi" to get it back to "messages from father to his son" ?
May be somebody can help me, I'm not clever enough to make an equation.
As I know, the vigenere equation basically like this :
Ci = Ek(Mi) = (Mi + Ki) mod 26
with E is the encryption and K is the key for the Encryption. And you know that the decryption from that encryption is like this :
Mi = Dk(Ci) = (Ci - Ki) mod 26
Now, I recreate the encryption using this formula :
C_i=E_k (M_i )=(∑_(i=0)^k▒(M_i+K_i ) + ∑_(i=k+1)^m▒〖(M_i+K_i))〗 mod 26
But, that's my problem is you can see my stupidity to create the equation. But I can convert the equation to the programming but not the opposite. I want to make the equation for analysis report. May be this add the unclear problem, and please don't tell me how to encrypt or decrypt that. May be a point to the basic math can enlighten me a little.