For separate partial alphabets the following results: For a merged alphabets, the encrypted text is "02468ACEacACEae024". If you are able to invent a fast factoring algorithm, you will not have to worry about a future job. } Multiplicative Cipher - Tutorial - scanftree Try to understand as much as possible first, then continue reading. So there is an infinite number of possible keys, but many will give identical messages, because for a $ k $ key, then the $ k + 26 $ key gives an identical cipher. We can also calculate all the possible keys for the Affine Cipher. That is: In fact, any character is stored as a number: i.e. This is important because if the key shares a factor with the plaintext, it can be easily broken by factoring in the key. Combining this fact with the fact that each key a possesses a decoding key a-1, the set of the good keys forms a commutative group with the unit element 1. From property 1) we know that ((2)=1 and ((13)=12, and consequently, ((2*13) = ((2)*((13) = 1*12 = 12 which is exactly property 3). For each character of the plain message, apply the following calculation: ($ 26 $ being the number of letters in the alphabet). Say, we want to encrypt the plain letter C=67. 3.0.4224.0. Take a moment now to verify the Rule for finding the decoding key a-1: 1) For a given good key a, find the unique 1 in the a-row, 2) From that 1 go all the way up that column, 3) The letters numerical equivalent that you hit on the very top is the inverse of a. Let s be such a reversible function. Thus, the encryption process is a Caesar cipher merged with a multiplication cipher. The statements while(cl!='~') and cout << cl; cin >> pl; are in charge of it. In fact, the sets of the encoding and decoding keys are identical. In conclusion, we can say that multiplicative cipher is a simple encryption technique that can be easily implemented. Equivalently stated, 105 divided by 26 leaves a remainder of 1. If 2 would be used as key, then C=2 -> 2*2 = 4 -> so the character C is encoded as an E. Analogous, P=15 -> 15*2 = 30 -> 30 modulo 26 = 4 -> the character P would also be encoded as an E.Therefore, it is not possible to determine if an E in a ciphertext corresponds to a C or a P. In order to achieve a unique matching only keys that are co-prime to the length of the alphabet can be used. Multiplication Cipher This table shows the occurances of the letters in the text (ignoring the case of the letters): This table shows how the text matches a normal probability to text (where 'E' has the highest level of occurance and 'Z' has the least). (Attacks). Say, the lower case plain letter c is entered, then the condition if ((pl>='a') && (pl<='z')) is fulfilled and the encryption is being executed by this one seemingly weird command cl='a' + (a*(pl -'a'))%26; Let me explain that to you in detail: First you need to know that each letter is stored as a number: i.e. Technically 1 too, but this would be no change from plaintext. where the operation of multiplication substitutes the operation of division by the modular multiplicative inverse. The plain letter c is stored as 103, however, I want the c to equal 2 in compliance with our translation a=0, b=1, c=2, etc. The basic modulation function of a multiplicative cipher in Python is as follows . Multiplicative cipher encryption|Multiplicative cipher|Multiplicative

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