We know for a fact that, if multiplicative inverse for a number exists then it lies in the range [0, M-1]. So the basic approach to find multiplicative inverse of A under M is:. The above implementation is a brute force approach to find Modular Multiplicative Inverse.

## Modular multiplicative inverse

Time Complexity is O Mwhere M is the range under which we are looking for the multiplicative inverse. However, this method fails to produce results when M is as large as a billion, say Can we do any better? There is one easy way to find multiplicative inverse of a number A under M. We can use fast power algorithm for that. Note that this method works when M is a prime number. Time Complexity of the above algorithm is also O log M.

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Table of Contents What is Multiplicative Inverse? What is Modular Multiplicative Inverse?

### Modular Multiplicative Inverse

How to find Multiplicative Inverse of a number modulo M i. Important points to note: Modulo inverse exists only for numbers that are co-prime to M. Ask it in the comments. Ravi Ojha.

Follow ivarojha.Previous matrix calculators: Determinant of a matrixMatrix TransposeMatrix MultiplicationInverse matrix calculator. This calculator finds modular inverse of a matrix using adjugate matrix and modular multiplicative inverse.

The theory, as usual, is below the calculator. In linear algebra an n-by-n square matrix A is called invertible if there exists an n-by-n matrix such that. This calculator uses adjugate matrix to find the inverse, which is inefficient for large matrices, due to its recursion, but perfectly suits us here.

Final formula uses determinant and the transpose of the matrix of cofactors adjugate matrix :. The cofactor of is where - determinant of a matrix, which is cut down from A by removing row i and column j first minor.

The main difference of this calculator from calculator Inverse matrix calculator is modular arithmetic. Modulo operation is used in all calculations and division by determinant is replaced with multiplication by modular multiplicative inverse of determinant, refer to Modular Multiplicative Inverse. Previous matrix calculators: Determinant of a matrixMatrix TransposeMatrix MultiplicationInverse matrix calculator This calculator finds modular inverse of a matrix using adjugate matrix and modular multiplicative inverse.

Modular inverse of a matrix. Share this page.During these challenging times, we guarantee we will work tirelessly to support you. We will continue to give you accurate and timely information throughout the crisis, and we will deliver on our mission — to help everyone in the world learn how to do anything — no matter what.

Thank you to our community and to all of our readers who are working to aid others in this time of crisis, and to all of those who are making personal sacrifices for the good of their communities. We will get through this together. Updated: December 30, Reader-Approved References. Inverse operations are commonly used in algebra to simplify what otherwise might be difficult.

For example, if a problem requires you to divide by a fraction, you can more easily multiply by its reciprocal. This is an inverse operation. Similarly, since there is no division operator for matrices, you need to multiply by the inverse matrix. Calculating the inverse of a 3x3 matrix by hand is a tedious job, but worth reviewing. You can also find the inverse using an advanced graphing calculator.

To find the inverse of a 3x3 matrix, first calculate the determinant of the matrix. If the determinant is 0, the matrix has no inverse.

Next, transpose the matrix by rewriting the first row as the first column, the middle row as the middle column, and the third row as the third column. Find the determinant of each of the 2x2 minor matrices, then create a matrix of cofactors using the results of the previous step.

Divide each term of the adjugate matrix by the determinant to get the inverse.

If you want to learn how to find the inverse using the functions on a scientific calculator, keep reading the article! Did this summary help you? Yes No. Log in Facebook Loading Google Loading Civic Loading No account yet? Create an account. We use cookies to make wikiHow great. By using our site, you agree to our cookie policy. As the COVID situation develops, our hearts ache as we think about all the people around the world that are affected by the pandemic Read morebut we are also encouraged by the stories of our readers finding help through our site.

Article Edit. Learn why people trust wikiHow. This article was co-authored by our trained team of editors and researchers who validated it for accuracy and comprehensiveness. Together, they cited information from 18 references. It also received 26 testimonials from readers, earning it our reader-approved status. Learn more Using a Calculator to Find the Inverse Matrix. Tips and Warnings. Related Articles. Article Summary. Method 1 of Modular Arithmetic - Cryptographer's Mathematics.

Mod-arithmetic is the central mathematical concept in cryptography. It is a very easy concept to understand as you will see. Use this page as a reference page and open it whenever you encounter any mod-calculations or mod-terminology that leave questions behind. So let's start:. Thus, "modular" or "mod arithmetic" is really "remainder arithmetic". More precise: We are looking for the integer that occurs as a remainder or the "left-over" when one integers is divided by another integer.

Let's do three examples:. Figure 1: Arithmetic MOD 3 can be performed on a clock with 3 different times: 0, 1 and 2.

You may have heard this anecdote about Gauss when he went to school: His Mathematics teacher tried to keep the bored genius busy, so he asked him to add up the first integers hoping that he would keep him quiet for a little while.

Do you know why? Great, we have the principle of Mod Arithmetic straight: To find the remainder simply divide the larger integer by the smaller integer.

This surely works for large numbers as well: I. What is the usage of Mod arithmetic? The same for your birthday and any other day as well: every week day will fall on the following weekday the next year. Notice again that we only care about the remainder 1 and not the completed 52 weeks in a year. In fact if a year would consist of only or or 15 or 8 days, we would still have the same "shift by 1" effect.

Apparently, solely the length of each week called the modulus determines the "shift by 1". Shift by 2 days. Integers that leave the same remainder when divided by the modulus m are somehow similar, however, not identical. Such numbers are called "congruent". For instance, 1 and 13 and 25 and 37 are congruent mod 12 since they all leave the same remainder when divided by However, they are not congruent mod Why not? The classical example for mod arithmetic is clock arithmetic: Look at the hour clock in your room.

You see 12 numbers on the clock. Here, the modulus is 12 with the twelve remainders 0,1,2. So, when you give the time you actually give a remainder between 0 and What time is it 50 hours after midnight?

Let's start simple: What time is it 10 hours after ? What time is it 22 hours after ? Ignoring a. Click here for a modular clock. Say it is 2 o'clock in New York, what time is it in L. That number must be between 0 and the modulus.Hot Threads. Featured Threads. Log in Register. Search titles only. Search Advanced search…. Log in. Support PF!

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### Find the inverse of modulus 26

For a better experience, please enable JavaScript in your browser before proceeding. What is the inverse of the 3x3 matrix mod Homework Statement What is the inverse of the 3x3 matrix mod 26? I then divided new matrix, by the determinate I found 17 by using the euclidean algorithm. However I am confused because even if I do this I do not get the answer in the book.

Scott Homework Helper. The Attempt at a Solution So I found all the cofactors and then took the transpose of the matrix. Ok cool so I did get the answer. You must log in or register to reply here. Related Threads on What is the inverse of the 3x3 matrix mod 26 Find the inverse of modulus Last Post Jul 15, 2. Replies 48 Views 11K. Inverse of a matrix. Last Post May 8, Replies 4 Views 2K. Comp Sci Fortran77 program to find the inverse of a matrix. Last Post Sep 7, Replies 1 Views 3K.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It only takes a minute to sign up. I am looking at cryptography, and need to find the inverse of every possible number mod Is there a fast way of this, or am i headed to the algorithm every time? Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Finding modular inverse of every number mod 26?

Ask Question. Asked 3 years, 11 months ago. Active 3 years, 11 months ago. Viewed 9k times. MathsPro MathsPro 1 1 silver badge 10 10 bronze badges. Active Oldest Votes. Then calculate the inverse of each one. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.

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**Multiplicative Inverse of 3 (mod 26)**

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## What is 3 inverse mod 26?

Question feed. Mathematics Stack Exchange works best with JavaScript enabled.This project for my Linear Algebra class is about cryptography. I will discuss a simple method of enciphering and deciphering a message using matrix transformations and modular arithmetic, and show how elementary row operations can sometimes be used to break an opponent's code.

The ciphers I will discuss are called Hill ciphers after Lester S. I will show an example of how a message is enciphered and deciphered using Hill ciphers, I will also briefly discuss how to break a Hill cipher using elementary row operations by giving an example from "Elementary Linear Algebra, Applications version, edition 6".

If I wanted to I could have assigned numerical values for all the other characters on a keyboard, but for simplicity I will only assign numerical values to the letters in the alphabet in this project. The following procedure shows the simplest Hill ciphers Hill 2-ciphersuccessive pairs of plaintext that are transformed into ciphertext by a 2 x 2 matrix A.

Here I have assigned numerical values to the alphabet:. Enciphering Step 3. Convert each plaintext pair p1p2 into a column vector p. Then form the plaintext matrix P of all our plaintext column vectors. To encipher the message we multiply our plaintext matrix P by our transformation matrix A to form the product A P.

The product of our matrix multiplication is the ciphertext matrix C. Enciphering Step 4. Now we convert each ciphertext vector into its alphabetical equivalent and write out our enciphered message. This was the encoding procedure, pretty simple, huh: Let's see how we decipher our enciphered message. Deciphering Step 1. Now we group the successive ciphertext letters into pairs and convert each ciphertext pair c1c2 into a column vector c.

Then form the ciphertext matrix C of all our ciphertext column vectors. Deciphering Step 2. Multiply the ciphertext matrix C with the inverse of our enciphering matrix A to obtain the deciphered message. Not too difficult, huh: NOTE: To use this procedure we have to understand the concept of modular arithmetic. In the 6 steps I showed you above, I chose not to include the modular arithmetic in the steps for simplicity.

However, modular arithmetic is important for this procedure to work. Keep reading and I'll show you why this is so important:. This is where Modular Arithmetic comes in handy. Our alphabet is given by non negative integers from 1, 2,What we do when we have over 26, is simply "wrapping around" the numbers from 27 to 52 to represent the 26 letters again, then we do the same thing from 53 to 78 etc.

The procedure of "wrapping" is quite general. It is the same procedure we use every noon and midnight when we begin again to number the hours 1, 2, etc. In a 24 hour system, is the same as pm and is pm.

How we do this mathematically is as follows: When we have integers greater than 26, we replace it by the remainder that results when this integer is divided by So if we have the number from the example above, we divide by 26 and the remainder is Now to the most important part of the concept of Modular Arithmetic for Hill ciphers. As mentioned in the procedure for enciphering and deciphering plaintext using a simple Hill-cipher above, we have to impose an additional condition for our transformation matrix A :.

The transformation matrix A must be invertible modulo m for this procedure to work. So when finding the inverse of our transformation matrix A we have to take mod m into consideration. The first thing we do is to group the letters into pairs of 2 letters. If we would do a Hill 3-cipher, we would group the letters in groups of 3 letters and use a 3 x 3 transformation matrix, but in this example we're using a Hill 2-cipher. For a Hill n-cipher, use n x n transformation matrix.

So, I have grouped the letters like this:.

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