def verify2(pk, sg, m): #？这段代码的含义不懂，对于公钥的修改？
from M2Crypto import BIO, RSA, EVP
bio = BIO.MemoryBuffer(pk)
rsa = RSA.load_pub_key_bio(bio)
pubkey = EVP.PKey()
pubkey.assign_rsa(rsa)
pubkey.reset_context(md='sha256')
pubkey.verify_init()
pubkey.verify_update(m)
return pubkey.verify_final(b64decode(sg))
