How to write a shift cipher (Caesar shift) algorithm in Java that will encrypt a given message (it may contain any letters, numbers, symbols, space) with a given shift key. It will also decrypt a given ciphertext with a given shift key.
Added by Deborah C.
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For example, if the shift key is 3, then the letter A will be replaced by D, B by E, and so on. Show more…
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To break a Vigenère cipher by recovering a plaintext message from the ciphertext message without having the key, the first step is to figure out the length of the key string. The second step is to figure out each character of the key string by deter- mining the corresponding shift. Exercises 21 and 22 deal with these two aspects. Suppose that when a long string of text is encrypted using a Vigenère cipher, the same string is found in the cipher-text starting at several different positions. Explain how this information can be used to help determine the length of the key.
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Suppose that the ciphertext DVE CFMV KF NFEUVI, REU KYRK ZJ KYV JVVU FW JTZVETV was produced by encrypting a plaintext message using a shift cipher. What is the original plaintext?
Suppose that the ciphertext ERC WYJJMGMIRXPC $\begin{array}{llll}\text { EHZERGIH } & \text { XIGLRSPSKC } & \text { MW } & \text { MRHMWXM- }\end{array}$ RKYMWLEFPI JVSQ QEKMG was produced by encrypting a plaintext message using a shift cipher. What is the original plaintext?
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