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Playfair cipher: Difference between revisions
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Decoded text is : HI DE TH EG OL DI NT HE TR EX ES TU MP
</pre>
=={{header|Nim}}==
{{trans|Java}}
<lang Nim>import pegs, strutils
type
Position = tuple[x, y: int]
Playfair = object
positions: array['A'..'Z', Position]
table: array[5, array[5, char]]
const None: Position = (-1, -1) # Default value for positions.
proc initPlayfair(key: string; jti: bool): Playfair =
for item in result.positions.mitems: item = None
var alphabet = key & "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
alphabet = if jti: alphabet.replace('J', 'I')
else: alphabet.replace("Q", "")
var k = 0
for ch in alphabet:
if result.positions[ch] == None:
result.table[k div 5][k mod 5] = ch
result.positions[ch] = (k mod 5, k div 5)
inc k
proc codec(playfair: Playfair; text: string; direction: int): string =
result.setLen(text.len)
for i in countup(0, text.high, 2):
var
(col1, row1) = playfair.positions[text[i]]
(col2, row2) = playfair.positions[text[i + 1]]
if row1 == row2:
col1 = (col1 + direction) mod 5
col2 = (col2 + direction) mod 5
elif col1 == col2:
row1 = (row1 + direction) mod 5
row2 = (row2 + direction) mod 5
else:
swap col1, col2
result[i] = playfair.table[row1][col1]
result[i + 1] = playfair.table[row2][col2]
proc encode(playfair: Playfair; text: string): string =
var
text = text
i = 0
while i < text.len:
if i == text.high:
if (text.len and 1) != 0:
text.add 'X'
elif text[i] == text[i + 1]:
text.insert("X", i + 1)
inc i, 2
result = playfair.codec(text, 1)
proc decode(playfair: Playfair; text: string): string =
result = playfair.codec(text, 4)
proc prompt(msg: string): string =
stdout.write msg
try:
result = stdin.readLine()
except EOFError:
echo ""
quit getCurrentExceptionMsg(), QuitFailure
when isMainModule:
var key: string
while key.len <= 6:
key = prompt("Enter an encryption key (min letters 6): ").toUpperAscii().replace(peg"[^A-Z]")
var text: string
while text.len == 0:
text = prompt("Enter the message: ").toUpperAscii().replace(peg"[^A-Z]")
var answer: string
while answer notin ["y", "n"]:
answer = prompt("Replace J with I? y/n: ").toLowerAscii()
let jti = (answer == "y")
let playfair = initPlayfair(key, jti)
let enc = playfair.encode(text)
let dec = playfair.decode(enc)
echo "Encoded message: ", enc
echo "Decoded message: ", dec</lang>
{{out}}
<pre>Enter an encryption key (min letters 6): Playfair example
Enter the message: Hide the gold...in the TREESTUMP!!!
Replace J with I? y/n: y
Encoded message: BMODZBXDNABEKUDMUIXMMOUVIF
Decoded message: HIDETHEGOLDINTHETREXESTUMP</pre>
=={{header|NetRexx}}==
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