I would like to do some testing with very weak RSA keys, like 128-bit or 256-bit to practice a little bit. But OpenSSL denies the creation of such weak keys with
$ openssl genrsa -out test.key 128
Error setting RSA length
40C7C155167F0000:error:1C8000AB:Provider routines:rsa_gen_set_params:key size too small:../providers/implementations/keymgmt/rsa_kmgmt.c:514:
I'm completely aware that such a key is about as secure as no encryption at all, because it can be factored in milliseconds, which is the whole point of the thing.
Aside from manually piecing together a weak key in a hex editor, how would you do such a thing?
Newer versions of OpenSSL do not support genrsa numbits below 512.
The default is 2048 and values less than 512 are not allowed.
I had no issue using openssl genrsa -out rsa.key 128 with LibreSSL 3.3.6
Here's some Python code that will generate keys; modify it as needed.
WARNING: These keys should never be used for anything.
import rsa
pubkey,privkey = rsa.newkeys(128)
print(pubkey.save_pkcs1('PEM').decode('UTF-8'))
print(privkey.save_pkcs1('PEM').decode('UTF-8'))
pubkey,privkey = rsa.newkeys(256)
print(pubkey.save_pkcs1('PEM').decode('UTF-8'))
print(privkey.save_pkcs1('PEM').decode('UTF-8'))
Output:
-----BEGIN RSA PUBLIC KEY----- MBgCEQCl/IGtHk0lD0CvdwOKbFtzAgMBAAE=
-----END RSA PUBLIC KEY----------BEGIN RSA PRIVATE KEY----- MGICAQACEQCl/IGtHk0lD0CvdwOKbFtzAgMBAAECEHp0P8LU8PrWWHEKUcKIQxEC CQv3mIVsiuS4yQIIDd7BlSarTFsCCQtwCEE1XYZ/KQIIBs84/O/aI4cCCQazNJyo Sa762g==
-----END RSA PRIVATE KEY----------BEGIN RSA PUBLIC KEY----- MCgCIQC0uFXIkpfJTJNMCsc4UTHvkfUGgs1dW3r9OLEBSnNCVwIDAQAB
-----END RSA PUBLIC KEY----------BEGIN RSA PRIVATE KEY----- MIGsAgEAAiEAtLhVyJKXyUyTTArHOFEx75H1BoLNXVt6/TixAUpzQlcCAwEAAQIh AJ9X/UNJhg4Wt7WPt1K/u/mPU9MwrXCqQVIPCXLrwuoRAhIA9DxAuEES2PbGPi5k 0hdwvk8CEAC9bNqhV9lSmjAn7XwlAXkCEgC7HsqrIFgzWGYsT9k4yXK8qwIPRsU1 hZQRsKfEmBZFDHpZAhEv3CG7tGSFobuQzMFxO4643A==
-----END RSA PRIVATE KEY-----
References
OpenSSL genrsa
Python RSA