Fix decrypt error with pkcs1 padding

[janispritzkau]

I am no expert in RSA cryptography, but was able to fix this issue by trial and error.

I found that the rsa_pkcs1_decrypt function sometimes throws a decryption error, particularly when the h variable in the rsadp function is negative. Switching the remainder operation to modulo seems to fix the problem. And all tests still work.

Should also fix issue #35.

[sonarqubecloud]

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[janispritzkau]

I would appreciate if this could be merged, even if this library is no longer maintained. I think there is still a need for third party crypto libraries as the web crypto API won't support older or unsecure encryption algorithms like RSA PKCS1 encryption/decryption or AES-128-CFB8.

[invisal]

Yes. I have merged the PR. Thanks for contribute. I was thinking of re-maintain it again as I have a bit more free time lately.

[janispritzkau]

You're welcome. I decided to re-implement the rsa pkcs1 encryption for my project anyway. A little trick I used is the jwk option in crypto.subtle.exportKey to avoid implementing the asn.1 ber encoding. (https://gist.github.com/janispritzkau/64b3cf0cd77978d269b2e59f5451c6a5)

Another issue in your implementation is a missing message length check in the pkcs1 encrypt function.