如何在python中验证签名文件

Question

背景

我已经使用openssl SHA256和私钥对文件进行了签名，如下所示：

with subprocess.Popen(
        # Pipe the signature to openssl to convert it from raw binary encoding to base64 encoding.
        # This will prevent any potential corruption due to line ending conversions, and also allows 
        # a human to read and copy the signature (e.g. for manual verification).
        'openssl dgst -sha256 -sign private.key sign_me.zip | openssl base64 > signature.sha256',
        stdout=subprocess.PIPE,
        stderr=subprocess.STDOUT,
        shell=True,
) as proc:
    out, _ = proc.communicate()

要求

1. 我需要使用signature.sha256并public_key.crt确认sign_me.zip尚未修改。
2. 兼容Python 3.2-3.4
3. 需要同时在Windows和Redhat上工作，并且不能保证OpenSSL将位于路径或已知位置。理想情况下，我想使用一个核心的Python模块，但是如果降低复杂性，我将考虑使用第三方模块。

我尝试过的

我已经做了很多搜索，试图弄清楚该如何做，但是我一直没有找到满意的答案。这是我尝试和/或研究过的东西的列表：

• 我可以通过以下shell命令手动验证签名。由于要求3，这不能作为永久解决方案。

  openssl dgst -sha256 -verify <(openssl x509 -in public_key.crt -pubkey -noout) -signature signature.sha256 sign_me.zip

• 我发现了这个问题，这几乎就是我想要做的。近两年没有得到答复，甚至没有发表评论。它提到了ssl python库，该库主要处理客户端/服务器证书和套接字。

• 这个问题似乎是使用加密库来验证“ SHA256withRSA和PKCS1填充”签名。不幸的是，它的目标是Python 2.7，此外，我无法在问题所引用verify()的Python 2.7 加密模块中找到方法文档。
• 我还发现了一个名为cryptography的第三方模块。关于Stack Overflow的共识似乎是这是用于加密等的最新/最好的模块，但是我找不到符合我要求的文档。

也许我缺少明显的东西？我在安全性/加密/散列方面还没有做很多工作，因此欢迎您提供反馈。

Answer 1

感谢Patrick Mevzek为我指出正确的方向。我最终使用密码模块找到了以下解决方案。我最终改变了我对文件签名的方式，以匹配以后将对其进行验证的方式。

密钥生成：

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa

# Generate the public/private key pair.
private_key = rsa.generate_private_key(
    public_exponent = 65537,
    key_size = 4096,
    backend = default_backend(),
)

# Save the private key to a file.
with open('private.key', 'wb') as f:
    f.write(
        private_key.private_bytes(
            encoding=serialization.Encoding.PEM,
            format=serialization.PrivateFormat.TraditionalOpenSSL,
            encryption_algorithm=serialization.NoEncryption(),
        )
    )

# Save the public key to a file.
with open('public.pem', 'wb') as f:
    f.write(
        private_key.public_key().public_bytes(
            encoding = serialization.Encoding.PEM,
            format = serialization.PublicFormat.SubjectPublicKeyInfo,
        )
    )

签名：

import base64
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import padding

# Load the private key. 
with open('private.key', 'rb') as key_file: 
    private_key = serialization.load_pem_private_key(
        key_file.read(),
        password = None,
        backend = default_backend(),
    )

# Load the contents of the file to be signed.
with open('payload.dat', 'rb') as f:
    payload = f.read()

# Sign the payload file.
signature = base64.b64encode(
    private_key.sign(
        payload,
        padding.PSS(
            mgf = padding.MGF1(hashes.SHA256()),
            salt_length = padding.PSS.MAX_LENGTH,
        ),
        hashes.SHA256(),
    )
)
with open('signature.sig', 'wb') as f:
    f.write(signature)

验证：

import base64
import cryptography.exceptions
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import padding
from cryptography.hazmat.primitives.serialization import load_pem_public_key

# Load the public key.
with open('public.pem', 'rb') as f:
    public_key = load_pem_public_key(f.read(), default_backend())

# Load the payload contents and the signature.
with open('payload.dat', 'rb') as f:
    payload_contents = f.read()
with open('signature.sig', 'rb') as f:
    signature = base64.b64decode(f.read())

# Perform the verification.
try:
    public_key.verify(
        signature,
        payload_contents,
        padding.PSS(
            mgf = padding.MGF1(hashes.SHA256()),
            salt_length = padding.PSS.MAX_LENGTH,
        ),
        hashes.SHA256(),
    )
except cryptography.exceptions.InvalidSignature as e:
    print('ERROR: Payload and/or signature files failed verification!')