Vigenere is polyalphabetic and wholly dependent on the key phrase. A great example of letting the system be known, but keeping your own secrets. Here is the table. Wikipedia has a decent description. Basically you have a key word or phrase.
Message to encode: This is the song that never ends...
So, I'll keep it simple and start with "S." I go to either the vertical or horizontal axis, doesn't matter which as long as you are consistent, and check bold "S" with bold "T." This gets "L." To decode, you go to bold "S" go down the row to "L" and trace up to "T." Simple? OK, yes, but when you do a lot...you tend to screw up.
But you learn tricks, like in decoding Keyphrase "B" paired with Cipher text"B" will always be "A." Applies to the whole alphabet. Some people tend to see that, but it took me actually using it to realize it. ;_; Or Keyphrase "B" paired with Ciphertext "A" will be "Z." Applies to all; if the ciper text letter appears directly before the keyphrase letter in the alphabet, the result it "Z." Blah blah blah.
Plaintext: This is the song that never ends
Key Phrase: I love the buckeyes five.
NHQKM VDZJA XALFL XSJBL FXTDO
MYHNK TUHBF GKPFI GBITS MSSME
HASXI NDLMW JTMNS DZBDS ESEDL
TUIJE WQQFI NEVZA VEVZV QCWYQ
WWQXE VEVZJ XDISY UDELH XFTJX
IYRDQ BYVUF XOVWT MUIKT UZFZX
AWTZM CNCRS JTCYS TLINI HKSBF
JOGMY FNOCX NJCPT PLWUC NYJSW
DIRJM MWODR ELETY NVLYZ LTUVO
But the message goes: Basically
you do the Vigenere in the order of HKVCV --> NHQKM --> MYHNK --> HASXI
--> TUIJE --> ASMFM
So then it's:
WWQXEIYRDQ AWTZM JOGMY DIRJM VEVZJ BYVUF CNCRS FNOCX MWODR XDISY XOVWT JTCYS NJCPT ELETY UDELH MUIKT TLINI PLWUC NVLYZ XFTJX UZFZX HKSBF NYJSW LTUVO
Easy enough, except the keyphrase didn't start at "I." I had to go through the whole combination of "Ilovethebuckeyesfive," "lovethebuckeyesfiveI," Etc. >.< It started with the "C" btw.
This does it much quicker, which I discovered after I'd already done every combination by hand.
Basically it was rife with spelling errors:
My method was to decode the first 4-5 letters and see if it could make sense.
Translation from Bad English:
In other news, am feeling well. Have a lot to do, but I can procrastinate a bit. ^_^
OK, LJ has eaten this post 5x. Good thing I copied it seconds before?