Convert private key to integer I have a random private key (compressed or uncompressed) 5HpHagT65TZzG1QDbnQCzdudnpknN7nA1SLEt4ZcxsH2SV92yqt or KwDiBf89QgGbjEmUcXPRwPuKPFnFECvJkvovGNiyjaujMCrQXy98. How do I convert this private key back to an integer?
Assuming the key is the posted  compressed WIF KwDiBf89QgGbjEmUcXPRwPuKPFnFECvJkvovGNiyjaujMCrQXy98:   


Decode the key you have using the encoder used (in this case base-58)
80-00000000000000000006f5d7d806edef2e1110b0b243f9a90c2aaaaaaaaaaaaa-01-098dbf37
Remove the extra bytes (version byte, compressed byte if present, checksum)
00000000000000000006f5d7d806edef2e1110b0b243f9a90c2aaaaaaaaaaaaa
Take the remaining bytes (in this case it must be 32 bytes) and convert it to an integer assuming it is positive and in big-endian (most significant value is stored first).
666666666666666666666666666666666666666666666666666666