Jorijn van der Graaf
e7a1825b50
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The imsd repo's package CI is now the only producer of the imsd apk. The image installs the exact registry package users get via 'apk upgrade' (pinned version + sha256 of the registry files), so the two can no longer diverge and the payload-parity rule between two packagings is gone. pmbootstrap has no knob for a third-party repository, and after the main 'apk add' it re-adds every package in its local packages dir by file path, which makes apk verify the package's own signature. Registry packages are signed with per-run keys nobody keeps (phones trust the registry-signed index), so apk-resign.py replaces the signature stream with one from this run's abuild key; control and data streams stay byte-identical and the identity checksum equals the registry's. Verified on the host with apk 3.0.8: originals UNTRUSTED, re-signed OK, checksums equal. The publish step skips imsd-*: those files came from the registry.
76 lines
2.7 KiB
Python
Executable file
76 lines
2.7 KiB
Python
Executable file
#!/usr/bin/env python3
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"""Re-sign an apk (v2 format) with another RSA key, in place.
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apk-resign.py <pkg.apk> <private key .rsa> <public key file name>
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An apk is three concatenated gzip streams: the signature tar, the control
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tar (.PKGINFO) and the data tar. The signature covers the control stream
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only, so replacing the first stream re-signs the package while its identity
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checksum (over the control stream) and its contents stay byte-identical.
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This is what abuild-sign does to the control segment when abuild packages.
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"""
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import gzip
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import io
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import subprocess
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import sys
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import tarfile
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import zlib
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DIGEST = {"RSA": "sha1", "RSA256": "sha256", "RSA512": "sha512"}
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def gzip_members(data):
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off = 0
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while off < len(data):
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d = zlib.decompressobj(31)
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d.decompress(data[off:])
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end = len(data) - len(d.unused_data)
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if end <= off:
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raise ValueError("gzip stream did not advance")
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yield data[off:end]
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off = end
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def first_entry_name(tar):
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"""Name of the first regular file in a tar stream, skipping pax headers."""
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off = 0
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while off + 512 <= len(tar):
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hdr = tar[off:off + 512]
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size = int(hdr[124:136].split(b"\0")[0].strip() or b"0", 8)
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if hdr[156:157] not in (b"x", b"g"): # not a pax extended/global header
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return hdr[:100].rstrip(b"\0").decode()
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off += 512 + (size + 511) // 512 * 512
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raise ValueError("no file entry in signature tar")
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def main(path, privkey, pubname):
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members = list(gzip_members(open(path, "rb").read()))
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if len(members) != 3:
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sys.exit(f"{path}: expected 3 gzip streams, found {len(members)}")
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old_sig, control, payload = members
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# keep the original digest type: the entry is .SIGN.<RSA|RSA256|RSA512>.<key>
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name = first_entry_name(gzip.decompress(old_sig))
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kind = name.split(".")[2] if name.startswith(".SIGN.") else ""
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if kind not in DIGEST:
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sys.exit(f"{path}: unexpected signature entry {name!r}")
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sig = subprocess.run(
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["openssl", "dgst", f"-{DIGEST[kind]}", "-sign", privkey],
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input=control, capture_output=True, check=True,
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).stdout
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buf = io.BytesIO()
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with tarfile.open(fileobj=buf, mode="w", format=tarfile.USTAR_FORMAT) as tar:
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info = tarfile.TarInfo(f".SIGN.{kind}.{pubname}")
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info.size = len(sig)
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info.mode = 0o644
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tar.addfile(info, io.BytesIO(sig))
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# like abuild-tar --cut: header + data blocks, no end-of-archive marker
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cut = 512 + (len(sig) + 511) // 512 * 512
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new_sig = gzip.compress(buf.getvalue()[:cut], mtime=0)
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with open(path, "wb") as f:
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f.write(new_sig + control + payload)
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if __name__ == "__main__":
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if len(sys.argv) != 4:
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sys.exit(__doc__)
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main(*sys.argv[1:])
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