使用pycrypto（RSA）签名和验证数据

这是文档中示例的丰富版本：

import Crypto.Hash.MD5 as MD5import Crypto.PublicKey.RSA as RSAimport Crypto.PublicKey.DSA as DSAimport Crypto.PublicKey.ElGamal as ElGamalimport Crypto.Util.number as CUNimport osplaintext = 'The rain in Spain falls mainly on the Plain'# Here is a hash of the messagehash = MD5.new(plaintext).digest()print(repr(hash))# 'xb1./Jxa883x974xa4xacx1ex1b!xc8x11'for alg in (RSA, DSA, ElGamal):    # Generates a fresh public/private key pair    key = alg.generate(384, os.urandom)    if alg == DSA:        K = CUN.getRandomNumber(128, os.urandom)    elif alg == ElGamal:        K = CUN.getPrime(128, os.urandom)        while CUN.GCD(K, key.p - 1) != 1: print('K not relatively prime with {n}'.format(n=key.p - 1)) K = CUN.getPrime(128, os.urandom)        # print('GCD({K},{n})=1'.format(K=K,n=key.p-1))    else:        K = ''    # You sign the hash    signature = key.sign(hash, K)    print(len(signature), alg.__name__)    # (1, 'Crypto.PublicKey.RSA')    # (2, 'Crypto.PublicKey.DSA')    # (2, 'Crypto.PublicKey.ElGamal')    # You share pubkey with Friend    pubkey = key.publickey()    # You send message (plaintext) and signature to Friend.    # Friend knows how to compute hash.    # Friend verifies the message came from you this way:    assert pubkey.verify(hash, signature)    # A different hash should not pass the test.    assert not pubkey.verify(hash[:-1], signature)