Different RSA public key generated on Android

Question

I was able to generate a public key in my Java desktop environment and I got something like this

Sun RSA public key, 1024 bits modulus: 101700973019391285593457598101942678753508114287289699162184623605939671495532511783006850112834969917970271633181351680298749946797462542179729127916916336425952724141383800466274935950042225686754068132826643586090512962724382324158485291344703936377718522573879330753020035687831145457530843148690890911921 public exponent: 65537

But on Android device, when I get the key as a string and use KeyFactory to generate the public key, I am getting this:

OpenSSLRSAPublicKey{modulus=90d3b5cefc50dc42828cee8d718876f7573b4c9287dddf808e73cb66266c2004165217f86d0f0192de0bb88b3aac2002303ee8b1c926e9bc54189a5ec5a12bb293df0b3c6ff2458a63098f712f0b72218ce301c38de3971ae8c6c646160a5e2e24dc07679e5a82ada1233ecf5eca3d0d1f483d1c9f059 a23deed537c670b70b1,publicExponent=10001}

There is discrepancy in the keys. I have tried SpongyCastle. I am still getting OpenSSL result on Android.

What am I missing?

Answer 1

There is no discrepancy between the keys. One is printed in base-16 (hexadecimal) whereas the other is printed in decimal. Just try the following code for reassurance:

BigInteger bi = new BigInteger(
    "90d3b5cefc50dc42828cee8d718876f7573b4c9287dddf808e73cb66266c2004165217f86d0f0192de0bb88b3aac2002303ee8b1c926e9bc54189a5ec5a12bb293df0b3c6ff2458a63098f712f0b72218ce301c38de3971ae8c6c646160a5e2e24dc07679e5a82ada1233ecf5eca3d0d1f483d1c9f059a23deed537c670b70b1",
    16);
System.out.println(bi.toString(10));

The result will be the same as your non OpenSSL key.

What's happening here is that your different platforms have different cryptographic providers that perform the crypto operations. The results will be the same, but there will be small idiosyncrasies that will be noticed, for example, when calling toString().