I was developing a crypto cracking challenge where the ultimate task is to factor a RSA key. To make the process feasible I want to use small key sizes (512 bits and lower). The challenge is a compiled binary for the ARM platform written in C.

Is there any open source libraries that I may use which supports small key sizes and preferably be used in embedded environments ?

Further, it would be great if it also can import OpenSSL generated keys in PEM or DER formats.

I tried using libtomcrypt but apparently it does not support key sizes of less than 1024 bits.

1 Answer 1


I finally settled for mbedTLS (formerly PolarSSL) by ARM Holdings.

It's open source, supports smaller key sizes and easily be used in embedded environments. It can import OpenSSL generated keys both in PEM or DER formats. An additional benefit of using this is it's highly modular which means we can leave out the components we do not need leading to smaller binary sizes.

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