Hi, On the topic of the relative difficulty/complexity of factoring RSA1024, one should be interested in the analysis contained in https://eprint.iacr.org/2010/006.pdf, where sieving for RSA1024 is benchmarked as 1000x that of RSA768, and later, due to improvements in polynomial selection http://www.ams.org/journals/mcom/2016-85-298/S0025-5718-2015... , 490x compared to the RSA768 result.