Tabula recta
Tabula recta is a cryptographic term invented by Johannes Trithemius in 1518. The tabula recta was a square table of alphabets, each one made by shifting the previous one to the left, like this:
|ABCDEFGHIJKLMNOPQRSTUVWXYZ|
--+--------------------------+---
A |ABCDEFGHIJKLMNOPQRSTUVWXYZ| 0
B |BCDEFGHIJKLMNOPQRSTUVWXYZA| 1
C |CDEFGHIJKLMNOPQRSTUVWXYZAB| 2
D |DEFGHIJKLMNOPQRSTUVWXYZABC| 3
E |EFGHIJKLMNOPQRSTUVWXYZABCD| 4
F |FGHIJKLMNOPQRSTUVWXYZABCDE| 5
G |GHIJKLMNOPQRSTUVWXYZABCDEF| 6
H |HIJKLMNOPQRSTUVWXYZABCDEFG| 7
I |IJKLMNOPQRSTUVWXYZABCDEFGH| 8
J |JKLMNOPQRSTUVWXYZABCDEFGHI| 9
K |KLMNOPQRSTUVWXYZABCDEFGHIJ| 10
L |LMNOPQRSTUVWXYZABCDEFGHIJK| 11
M |MNOPQRSTUVWXYZABCDEFGHIJKL| 12
N |NOPQRSTUVWXYZABCDEFGHIJKLM| 13
O |OPQRSTUVWXYZABCDEFGHIJKLMN| 14
P |PQRSTUVWXYZABCDEFGHIJKLMNO| 15
Q |QRSTUVWXYZABCDEFGHIJKLMNOP| 16
R |RSTUVWXYZABCDEFGHIJKLMNOPQ| 17
S |STUVWXYZABCDEFGHIJKLMNOPQR| 18
T |TUVWXYZABCDEFGHIJKLMNOPQRS| 19
U |UVWXYZABCDEFGHIJKLMNOPQRST| 20
V |VWXYZABCDEFGHIJKLMNOPQRSTU| 21
W |WXYZABCDEFGHIJKLMNOPQRSTUV| 22
X |XYZABCDEFGHIJKLMNOPQRSTUVW| 23
Y |YZABCDEFGHIJKLMNOPQRSTUVWX| 24
Z |ZABCDEFGHIJKLMNOPQRSTUVWXY| 25Trithemius used the tabula recta to define a polyalphabetic cipher which was equivalent to Leon Battista Alberti's cipher disk. The tabula recta is often referred to in discussing pre-computer ciphers, including the Vigenère Cipher and Vigenère's less well-known (but much stronger) autokey cipher. All polyalphabetic ciphers based on Caesar ciphers can be described in terms of the tabula recta.
| Classical cryptography |
| Ciphers: ADFGVX | Affine | Atbash | Autokey | Bifid | Book | Caesar | Permutation | Playfair | Polyalphabetic | Running key | Substitution | Transposition | Vigenère |
| Cryptanalysis: Frequency analysis | Index of coincidence Misc: Cryptogram | Polybius square | Scytale | Straddling checkerboard | Tabula recta |