playfair is fairly easy to break using frequency analysis, especially wi
th modern computers. Because
the same digram will always encode to
the same pair of letters, it doesn't significantly increase
the brute force necessary. If you have a sample of plaintext and its equivalent ciphertext key extraction is trivial. If you have enough ciphertext frequency analysis is straight froward. Cribs can also be used, as wi
th any substitution cipher. For example, in any leng
thy english text
the letters th will appear very often.
Now if you want a real challenge, try this cipher I recently sent to a friend at NSA

9a af 4e 54 67 03 b7 ab 23 4a 01 eb ff 5c e0 7b 4f e6 39 2f fa 5e 97 43 ee 05 eb 3e a6 28 7e 7f c6 cf f3 e5 a1 b4 62 09 fd e2 56 1a 82 e7 59 c4 84 49 32 23 67 bf 87 7f 18 b8 32 41 c3 4b 82 c3 af c1 fc 53 ad ce 97 ad 15 15 5a 0f f7 2d b9 97 8a 6e d2 7f 01 42 f7 6f 7a a2 ab 89 9a e1 57 6d 9b f2 46 67 d5 f8 2a 2f 8d db aa 48 22 5d 22 23 5f 06 c7 97 fc b5 52 38 26 14 8c 15 7a 87 fe 5b 33 32 88 80 0f dd 9c b0 14 b3 19 3b 43 b9 53 8b 33 8b 13 83 fc 14 b3 dc 67 40 26 d5 0b cf 2a ed da c1 44 a6 88 07 f2 06 43 50 0a ce 6d b7 0b cb 78 90 4f 76 54 bd f7 9e 27 3e e5 a5 81 43 1c 8b b1 b7 34 b7 36 1e 2a c0 f4 8f cb dd b5 f8 c2 e3 0d ed 80 0e 97 d6 b0 09 d2 7a bc 44 07 d6 c8 df 56 70 b3 e8 77 52 d5 05 bd 26 50 c5 d3 79 38 7d 12 45 f9 d8 08 3e 54 78 e7 5d ce c4 3f 59 4f a9 4c bf 22 83 6d 31 19 07 0e e7 28 72 ef 29 45 20 0e f6 48 de 9c 8b 4b 25 04 27 16 3b 9b 30 a8 ff 58 0e 05 4c ab 13 a9 e8 62 e4 17 ec e8 d7 d2 f2 e8 0b fe 9c 65 28 22 77 a2 32 95 a4 ed de 34 0d c3 3d 03 71 26 37 82 30 e2 1b 08 84 3e 5b c0 91 c2 c3 65 32 f7 9e 10 7a 5a 75 21 2f 68 c3 86 d5 72 24 a5 24 44 1e 1c 7e 9a d9 ac f8 48 0b f7 6e 48 6e 0d 4e 82 c5 72 f4 37 f1 9f 47 0f db c6 2f 38 3f 94 56 25 4d e0 f1 76 9f ee 9b 92 9e dc f4 a0 86 63 06 f7 e2 f7 09 4b 2f 18 bd fe 7a 55 0e 97 3d 1f 8e df ef 2d b3 e7 6f f4 ad 64 ec e3 4f 10 8c bf f0 71 9a b1 11 a2 ff 87 f3 f5 c1 e3 ff a6 2a e1 b3 c0 ea d1 91 6a c3 35 16 28 e0 f4 cd b4 47 cb 20 0a 69 93 6d 13 b0 44 82 a5 cd 43 ee d2 1e 97 4e d1 ec 5e 34 c7 d5 80 84 43 11 c7 32 d9 c6 da e7 9c 36 e3 75 fb 22 74 af 7e 57 6f 73
It is text, taken from a classic novel.
It is English
The cipher is not a one time pad