Encryption of Gronsfeld
The encryption of Gronsfeld emerged as an enhancement to the encryption, Vigenère, as that was susceptible to an analysis cryptic with certain conditions laid down. To evaluate some features, it was possible to define the length of the key, and then, when parsing the rows of letters, enciphered by the same row of the table, one could employ a standard method based on the frequency of certain letters of the language
The first to make a successful attack in the modification of the encryption Vigenère in 1854, was Charles Babbage, a pioneer of computing, but the analysis was released nine months later by another researcher, Friedrich Kasiski
Strange as it may seem, this helped to strengthen it, resulting in the encryption of Gronsfeld. One of the improvements was the use of the word key, which is equal to the length of the message itself, thus eliminating the possibility of a frequency analysis
However, this update brought another vulnerability: the use of text-sensitive as a key phrase, contributed to the criptoanalista statistical information about the key, serving as a track to the point of wanting to decipher the text
As it is based on the encryption Vigenère, is also a substitution encryption simple polyalphabetic. This means that using more than one alphabet cipher to put in the key the message and that it changes from one to the other as it passes from a letter of the clear text to another. That is to say that you should be a set of alphabets encrypted and a way to match each letter of the original text with one of them
The number of alphabets encryption is limited to 10, coded from 0 to 9 and the key is generated with a combination of these digits, without repetitions. Alters the frequency of the letters of the text, since for example the letter more current in English, E, is encrypted differently according to their position in the original text
Throughout this article for simplicity I will use standard English alphabet 26 letters:
\tiny\begin{pmatrix} 0& 1& 2& 3& 4& 5& 6& 7& 8& 9& 10& 11& 12& 13& 14& 15& 16& 17& 18& 19& 20& 21& 22& 23& 24& 25 \\ A& B& C& D& E& F& G& H& I& J& K& L& M& N& O& P& Q& R& S& T& U& V& W& X& Y& Z \\ \end{pmatrix}
And the next box corresponding to the encryption of Gronsfeld
this box is not the only possible one, it has been used as an offset to the first 9 prime numbers, and may use another method to create the 10 alphabets
Example of encryption of Gronsfeld
We have the following message that we want to encrypt:
C=MESSAGE SENT YESTERDAY
We take as key:
K = 1203456987
It is advisable that the key is larger than the message. We put together a message and a key, repeating as many times as necessary the key
\tiny\begin{pmatrix} M& E& S& S& A& G& E& S& E& N& T& Y& E& S& T& E& R& D& A& Y \\ 1& 2& 0& 3& 4& 5& 6& 9& 8& 7& 1& 2& 0& 3& 4& 5& 6& 9& 8& 7 \\ \end{pmatrix}
We go to the table of encryption, and we take the row of the first key number in the table of Gronsfeld and the column of the first letter of the message. The intersection of both will be the letter that will be used for encryption. We will repeat the process until you get the encrypted message
So we is that the encrypted message is:
M=PJUZLTVUBGWDGZERIFXR
We can decipher the M previous
We go to the table of encryption, and we take the row of the first key number in the table of Gronsfeld and looking for the first letter of the message. The row of the intersection of both will be the letter that will be used in the decrypted message. We will repeat the process until you get the message clear
\tiny\begin{pmatrix} 1& 2& 0& 3& 4& 5& 6& 9& 8& 7& 1& 2& 0& 3& 4& 5& 6& 9& 8& 7 \\ P& J& U& Z& L& T& V& U& B& G& W& D& G& Z& E& R& I& F& X& R \end{pmatrix}
Getting the original C:
C=MESSAGESENTYESTERDAY