Vigenère cipher is an encryption algorithm developed in 1553 and was considered uncrackable until the middle of the 19th century.
Application:
In order to encrypt text, you need to choose a word, W, and the encryption table.
Now, you encrypt the mth letter in the text you want to encrypt using a letter from the word W that was chosen before according to the following formula:
Em = L(m % n)
where:
m — the serial number of the letter n the text
Em — the letter for the m letter in the text
n — the length of w
L — the letter in w in the specified index.
Now, in the encryption table you go to (Em,Tm) (Tm is the m letter you encrypt), and write the letter that's written there, instead of the original letter.
The encryption table
|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| ------------------------------------------------------ a|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| ------------------------------------------------------ b|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|a| ------------------------------------------------------ c|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b| ------------------------------------------------------ d|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c| ------------------------------------------------------ e|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d| ------------------------------------------------------ f|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e| ------------------------------------------------------ g|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f| ------------------------------------------------------ h|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g| ------------------------------------------------------ i|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h| ------------------------------------------------------ j|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i| ------------------------------------------------------ k|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j| ------------------------------------------------------ l|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k| ------------------------------------------------------ m|m|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l| ------------------------------------------------------ n|n|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m| ------------------------------------------------------ o|o|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n| ------------------------------------------------------ p|p|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o| ------------------------------------------------------ q|q|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p| ------------------------------------------------------ r|r|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q| ------------------------------------------------------ s|s|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r| ------------------------------------------------------ t|t|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s| ------------------------------------------------------ u|u|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t| ------------------------------------------------------ v|v|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u| ------------------------------------------------------ w|w|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v| ------------------------------------------------------ x|x|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w| ------------------------------------------------------ y|y|z|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x| ------------------------------------------------------ z|z|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|
More information at Wikipedia under Vigenère cipher.
