在Python中验证X509证书的签名

Question

我有一把 RSA 公钥和一个已签名的 X509 证书。我该如何检查该密钥是否签署了该证书？（我的示例恰好是自签名证书。）

以下是我现在正在做的事情：

使用 OpenSSL 命令行生成自签名证书并将其转换为 DER 编码。

（在我的实际应用程序中，我期望得到 DER 编码）

openssl req -x509 -newkey rsa:2048 -keyout selfsigned.key -nodes -out selfsigned.cert -sha256 -days 1000
openssl x509 -outform der -in selfsigned.cert -out self.der

将它解码为 Crypto.Util.asn1.DerSequence 实例。

>>> from Crypto.Util.asn1 import DerSequence
>>> from Crypto.PublicKey import RSA
>>> der = open('self.der').read()
>>> cert = DerSequence()
>>> cert.decode(der)
905L
>>> # according to RFC5280, this is a 3-length sequence:
>>> # tbsCertificate, signatureAlgorithm, signatureValue
>>> # "tbs" == "to be signed"
>>> len(cert)
3

然后我取出RSA公钥：

>>> tbscert = DerSequence()
>>> tbscert.decode(cert[0])
>>> subjectPublicKeyInfo = tbscert[6]
>>> rsa_key = RSA.importKey(subjectPublicKeyInfo)
>>> >>> rsa_key
<_RSAobj @0x7fb27287d128 n(2048),e>

然后我取出签名

这非常令人烦恼。我再次使用另一个库对DER进行解码，因为这个库给我提供了“比特串”编码的签名值更方便的表示方法。目前，我将该值的二进制字符串表示复制并粘贴到int()中以获取long（RSA.verify()方法所期望的）。

>>> from pyasn1_modules import  rfc2437,rfc2459
>>> from pyasn1.codec.der import decoder
>>> cert2,rest = decoder.decode(der, asn1Spec=rfc2459.Certificate())
>>> sig_bits = cert2.getComponentByName("signatureValue")
>>> sig_bits
BitString("'10101110101100111010100000111001000110111111101001110000100111110111011111111110011010110101001001110110111011011001110001010000111001001001110111001110011101000000100000001100001101000111000110010100110101000110111101110001011011001001100011110011010101011100000001010111101110111001110011010011110101101001110101110100011111011111110001110001110100000110110100010000001010111010000100101110101001110000111001100010011110110100101001010000101001110101101111100111001111000010111001110000000101000000011110011110000110000101101101110110101101110101011110101111111000101011001000010000110100111111001011111100110011011011001001111110000000110100000001101000011010010100001100110100001001000111001011111100000011000101001100001010101001111000001010100101010101000100001000100011101111100101010010001111001110100001011110101100010111001010100010001011100000100101110001011101100010010111100010111110010010110111111100100100101010010000000010001011111110011000011000101000001000000000000011111101110010101100100000010111111110101000110010101111100101011101000010010110101000101101110001001101101000110101110011101011111100010000101001111011100100100010101001011011110001110000000000010011011111011110100000111001100010100000100001101111110010000111100110110110000001010010110011010111100101110101000001111001010011101001101101101101011000100010011110000101010110111011100010100011110101100110101011010111000011111000001111111111000101101101011110010111100101011100010000111011101101010101001011101101111011001001110000010011001111010001011110000011001011000110100011100000100100111000111100000010000001001001010001100000010011110100000111010010100001101001111111001111110111010001101010110100001100111010101000010000101000000111100001001001000100011100110010110101001110111101000101101011011100000010010000100111001100001110010101000100000010010111110001100011110010000100001000101100011000011000110010110011100010100010111011011111111010000001001100000100011010000000110111100111010101001110101000011111011000100010111101100110100010101111000110111110'B")
>>> bit_string = '10101110101100111010100000111001000110111111101001110000100111110111011111111110011010110101001001110110111011011001110001010000111001001001110111001110011101000000100000001100001101000111000110010100110101000110111101110001011011001001100011110011010101011100000001010111101110111001110011010011110101101001110101110100011111011111110001110001110100000110110100010000001010111010000100101110101001110000111001100010011110110100101001010000101001110101101111100111001111000010111001110000000101000000011110011110000110000101101101110110101101110101011110101111111000101011001000010000110100111111001011111100110011011011001001111110000000110100000001101000011010010100001100110100001001000111001011111100000011000101001100001010101001111000001010100101010101000100001000100011101111100101010010001111001110100001011110101100010111001010100010001011100000100101110001011101100010010111100010111110010010110111111100100100101010010000000010001011111110011000011000101000001000000000000011111101110010101100100000010111111110101000110010101111100101011101000010010110101000101101110001001101101000110101110011101011111100010000101001111011100100100010101001011011110001110000000000010011011111011110100000111001100010100000100001101111110010000111100110110110000001010010110011010111100101110101000001111001010011101001101101101101011000100010011110000101010110111011100010100011110101100110101011010111000011111000001111111111000101101101011110010111100101011100010000111011101101010101001011101101111011001001110000010011001111010001011110000011001011000110100011100000100100111000111100000010000001001001010001100000010011110100000111010010100001101001111111001111110111010001101010110100001100111010101000010000101000000111100001001001000100011100110010110101001110111101000101101011011100000010010000100111001100001110010101000100000010010111110001100011110010000100001000101100011000011000110010110011100010100010111011011111111010000001001100000100011010000000110111100111010101001110101000011111011000100010111101100110100010101111000110111110'
>>> len(bit_string)
2048
>>> sig_long = int(bit_string, 2)
22054057292543290008991218833668878365914778519473463062473060546762899555976103489048033910135613221569150796460758806399269198735780309519101363051388009338597879536630494212385605300708879019160215628821483902624509955250980351374010304684207884550324020859785789812498991361733361061223150200173076263554090698006436248180914014712709890577579243572383188197634606581121383593473899061397708617253275982314075801792358481980896751043809539358665686019958496887281091997170247998458556812030465091755579654010246474389968142047627934047174316731806191431717418170761689395728146445291177267566370799362894264463806L

接下来我计算“待签名证书”的SHA256哈希值：

>>> import Crypto.Hash.SHA256
>>> comp_hash = Crypto.Hash.SHA256.new(cert[0]).digest()
>>> comp_hash
'\xa3t\x84\xd6\xf5\xfe\x16\xb9\xdb(&\x12\xb3m^+\x94\xa7bZ\xf9s\xf7\xbay\xa1j\xa3Y\xea\xa8\x7f'

然后verify()方法告诉我签名不匹配。

>>> rsa_key.verify(comp_hash, (sig_long, None))
False

我希望有更好的方法（这种方法甚至无法使用），但我已经花费数小时查看PyCrypto和PyOpenSSL，但没有找到它。

编辑

几年前的类似问题在Stack Overflow上没有答案：验证SSL/X.509证书是否由另一个证书签名。

- joelanders

Answer 1

我想实现这个的一种方法是创建一个只包含与我要检查的公钥相对应的一个证书的X509StoreContext。

>>> from OpenSSL import crypto
>>> x509_self_signed # already loaded
<OpenSSL.crypto.X509 object at 0x7fcc4049c9b0>
>>> cert_store = crypto.X509Store()
>>> cert_store.add_cert(x509_self_signed)
>>> store_ctx = crypto.X509StoreContext(cert_store, x509_self_signed)
>>> store_ctx.verify_certificate()
>>> # ^ that raises an exception if it fails to verify

verify_certificate() 是在一年多前才被添加到 PyOpenSSL 中的，这可能是为什么很难找到它的原因...https://github.com/pyca/pyopenssl/pull/155

- joelanders

---

如何加载证书？ - wick