hashlib：在计算签名哈希期间被杀死

Question

我正在尝试运行 Android check_ota_package_signature.py https://android.googlesource.com/platform/build/+/refs/heads/main/tools/releasetools/check_ota_package_signature.py

在低端计算机上。该程序用于检查 Android OTA 更新的签名。不幸的是该程序正在被杀死。恕我直言，相关部分是：

with open(package, 'rb') as package_file:
 package_bytes = package_file.read()
length = len(package_bytes)
footer = bytearray(package_bytes[-6:])
signature_start_from_end = (footer[1] << 8) + footer[0]
signature_start = length - signature_start_from_end
comment_len = (footer[5] << 8) + footer[4]
signed_len = length - comment_len - 2

comment_len = (footer[5] << 8) + footer[4]
signed_len = length - comment_len - 2

print('Package length: %d' % (length,))
print('Comment length: %d' % (comment_len,))
print('Signed data length: %d' % (signed_len,))
print('Signature start: %d' % (signature_start,))

use_sha256 = CertUsesSha256(cert)
print('Use SHA-256: %s' % (use_sha256,))

h = sha256() if use_sha256 else sha1()
h.update(package_bytes[:signed_len])

package_digest = h.hexdigest().lower()

h.update(package_bytes[:signed_len]) 被杀死。我的理解是，这是由于内存不足而发生的，因为大约的文件。一次读取1.1GB。如何更改程序以小块读取文件，这样我就不会遇到这个问题？

我希望验证签名。相反，我收到以下消息：

Package length: 1182903653
Comment length: 1983
Signed data length: 1182901668
Signature start: 1182901688
Use SHA-256: True
Killed

Answer 1

使用

mmap()

将文件映射到虚拟内存，然后让操作系统将虚拟内存分页进出物理内存，是减少内存需求的一种方法（与运行大型

read()

的原始行为相比）将整个文件复制到新分配的内存中，该内存没有磁盘支持，并且除非定义了足够的交换区，否则无法调出）。

#!/usr/bin/env python3

import mmap
import sys
from hashlib import sha256, sha1

with open(sys.argv[1], 'rb') as f:
    with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) as mm:
        length = len(mm)
        footer = bytearray(mm[-6:])
        signature_start_from_end = (footer[1] << 8) + footer[0]
        signature_start = length - signature_start_from_end
        comment_len = (footer[5] << 8) + footer[4]
        signed_len = length - comment_len - 2

        comment_len = (footer[5] << 8) + footer[4]
        signed_len = length - comment_len - 2

        print('Package length: %d' % (length,))
        print('Comment length: %d' % (comment_len,))
        print('Signed data length: %d' % (signed_len,))
        print('Signature start: %d' % (signature_start,))

        h = sha256()

        ## slower, but more explicit about only dealing with small chunks at a time
        current_pos=0
        block_size=4096
        while current_pos < signed_len:
            block_end = min(current_pos+block_size, signed_len)
            h.update(mm[current_pos:block_end])
            current_pos = block_end
            gc.collect()

        ## faster but depends on CPython implementation details
        # h.update(mm[:signed_len])

        print(h.hexdigest().lower())