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「add-apt-repository」對於惡意網路（「MITM」）是否安全？

tag-icon • tag-icon ubuntu security apt
「add-apt-repository」對於惡意網路（「MITM」）是否安全？

當我運行它時，輸出有點可疑：

# add-apt-repository -y ppa:ansible/ansible
gpg: keyring `/tmp/tmp85zwje4_/secring.gpg' created
gpg: keyring `/tmp/tmp85zwje4_/pubring.gpg' created
gpg: requesting key 7BB9C367 from hkp server keyserver.ubuntu.com
gpg: /tmp/tmp85zwje4_/trustdb.gpg: trustdb created
gpg: key 7BB9C367: public key "Launchpad PPA for Ansible, Inc." imported
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
OK

我們不應該通過如此短的字串來識別鍵，因為衝突的 keyid 可以在5秒以內。

答案1

不用擔心這個輸出。

儘管 GPG 會列印過時的 keyid，但 apt-add-repository 實際上是使用其 160 位元指紋來取得金鑰。 （指紋似乎是透過 HTTPS 取得的）。

https://bazaar.launchpad.net/~ubuntu-core-dev/software-properties/main/annotate/head:/softwareproperties/ppa.py#L163

def verify_keyid_is_v4(signing_key_fingerprint):
    """Verify that the keyid is a v4 fingerprint with at least 160bit"""
    return len(signing_key_fingerprint) >= 160/8


class AddPPASigningKey(object):
    " thread class for adding the signing key in the background "

    GPG_DEFAULT_OPTIONS = ["gpg", "--no-default-keyring", "--no-options"]

    def __init__(self, ppa_path, keyserver=None):
        self.ppa_path = ppa_path
        self.keyserver = (keyserver if keyserver is not None
                          else DEFAULT_KEYSERVER)

    def _recv_key(self, keyring, secret_keyring, signing_key_fingerprint, keyring_dir):
        try:
            # double check that the signing key is a v4 fingerprint (160bit)
            if not verify_keyid_is_v4(signing_key_fingerprint):
                print("Error: signing key fingerprint '%s' too short" %
                    signing_key_fingerprint)
                return False

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