Security and Cryptography (S2, 2014)

Homework 2 - Break Classical Ciphers

Below I provide several ciphertexts and in some cases some hints (such as algorithm used). Try to find the plaintext and key.

This task is not required and should only be attempted after you have done the quiz and have a good understanding of the lecture topics. I suggest you only attempt it when you have some free time.

Email me your answer, as well as a short description of how you found it, when you have found a plaintext. You can do them in any order. Although there may be websites that will automatically solve these for you, you will have more fun if you attempt to solve it yourself (although you may still use a computer).

All plaintext messages are in English, have punctuation removed and are in lowercase (i.e. the character set is a-z). If there are spaces/linefeeds in the ciphertext below, then it is just for convenience of presenting on this web page; the ciphertext that you analyse has no spaces or linefeeds.

Some general hints on performing attacks may be found by reading about frequency analysis and brute force.

Ciphertext 1

Ciphertext:

jxyigkuijyedyijeeuqiooeksqduyjxuhteqrhkjuvehsuqjjqsaehiecurqiysbujjuhvhugkudsoqdqboiyijevydtjxuauoqdtfbqydjunjdunjjycucqauyjxqhtuh

Hint: general Caesar cipher was used.

Ciphertext 2

Ciphertext:

 cohhdltormargyeyghseutyrisoomecnipastfrscoiotptuaitumcn

Hint: rail fence cipher was used.

Ciphertext 3

Ciphertext:

uanynsfalgrcreireyetoniabcsteeocvteerkehkxttvitp

Hint: rows/columns cipher was used.

Ciphertext 4

Ciphertext:

adxnrdvbnxdradcgbxjwfvdrqfswadbxkqfswnkghfwghbkdxuvivkgsbvvgslagjnxjghkogsfjgafmmhggbxjfwgxvfnhqgvfmkebhgjgpgafwsgxkbxjjdvkhdlnkdfxkogsbdxmfhsfmjdvkhdlnkdfxbhgadxnrjdvkhdlnkdfxvkogjgmdxdxuqfswfxgxkfmadxnrdvkogadxnrcghxgabxfwghbkdxuvivkgscghxgamdhvkhgagbvgjliadxnvkfhpbajvadxnvkfhpbajvdvbmdxxdvobsghdqbxvfmkebhggxudxggheofebvkogwhdxqdwbamfhqglgodxjkogjgpgafwsgxkfmkogadxnrcghxgaogabkghlgqbsgkogqodgmbhqodkgqkfmkogadxnrcghxgabxjxfebqkvbvkogwhftgqkvqffhjdxbkfhogbavfqhgbkgjkoghgpdvdfxqfxkhfavivkgsudkbvegaabvkogjdpdxuafuvfmkebhgvnlvnhmbqghdqobhjvkbaasbxfmkgxcxfexliodvdxdkdbavhsvdvbxbsghdqbxvfmkebhgmhggjfsbqkdpdvkbxjqfswnkghwhfuhbssghogqbswbduxvmfhvfmkebhgkflgjdvkhdlnkgjdxbsbxxghvnqokobkbnvghhgqgdpdxudkadcgedvghgqgdpgvedkodkkogmhggjfsvkfnvgvknjijdvkhdlnkgbxjsfjdmikobkvfmkebhgvfmkebhgkobkgxvnhgvkogvgmhggjfsvdvkghsgjmhggvfmkebhgogdvlgvkcxfexmfhabnxqodxukoguxnwhftgqkmfnxjdxukogmhggvfmkebhgmfnxjbkdfxjgpgafwdxukoguxnqfswdaghqfaagqkdfxbxjuxngsbqvbxjehdkdxukoguxnugxghbawnladqadqgxvg

Hint: mono-alphabetic cipher was used.

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