Msieve Factorizer

Number to factorize
Status of factorization
Example numbers to factorize
Found factors:
Factorized number:

    The Msieve Factorizer can be used to factor large integers into prime numbers using the quadratic sieve algorithm.

    Enter a number into the factorization input field and press the „Factorize“ button to start the process.

    You can also click on one of the example numbers in order to put its value into the input field.

    Technical background

    Due to the fact that factoring large numbers is a very CPU intense process, the Msieve Factorizer uses WebAssembly technology [3] in order to achieve appropriate performance in this client-side web application. Only one single CPU core is used for the calculation process.

    The calculation is performed by using the Open Source application Msieve 1.53, which has been ported to WebAssembly for this purpose [1].

    About Msieve

    Msieve [2] is a C library implementing a suite of algorithms to factor large integers. The relevant algorithm for this CTO site is the self-initializing quadratic sieve (QS) [4].


    In case you are interested in using the quadratic sieve algorithm with full performance, check out CrypTool 2 [5]. You'll find an implementation of the QS algorithm in the template "Factorization with Quadratic Sieve (QS)".


    Msieve Factorizer CTO site: Sven Rech
    Msieve WebAssembly port [1]: Sven Rech
    Msieve [2]: Jason Papadopoulos


    [1]: Msieve-Web (port to WebAssembly):
    [2]: Msieve:
    [3]: WebAssembly:
    [4]: Quadratic Sieve: