GPG - 在不创建信任链的情况下验证签名？

Question

是否可以要求 gpg（或 gpg4win）仅验证文件是否由特定公钥文件签名，而无需导入、签名和信任该密钥？

即类似的东西

gpg --using-key pubkey.txt --verify message.txt

而不是必须创建自己的私钥然后再做

gpg --import pubkey.txt 
gpg --lsign-key [name within pubkey.txt]
# ... something to do with choosing trust levels
gpg --verify message.txt

Answer 1

您必须拥有公钥才能验证使用相应私钥进行的签名，但您不必对密钥进行签名，甚至无需在本地签名。在这种情况下，您将收到来自 GPG 的警告，指出密钥不受信任。

这是我使用由我自己的密钥签名的文件进行的测试，但在未导入密钥的系统上：

[ben@seditious tmp]$ gpg -v --verify thing.txt.gpg 
gpg: original file name='thing.txt'
gpg: Signature made Thu 26 Sep 2013 06:51:39 AM EST using RSA key ID 35C7553C
gpg: Can't check signature: public key not found
[ben@seditious tmp]$ gpg -v --status-fd 1 --verify thing.txt.gpg 
gpg: original file name='thing.txt'
gpg: Signature made Thu 26 Sep 2013 06:51:39 AM EST using RSA key ID 35C7553C
[GNUPG:] ERRSIG 7FF2D37135C7553C 1 10 00 1380142299 9
[GNUPG:] NO_PUBKEY 7FF2D37135C7553C
gpg: Can't check signature: public key not found
[ben@seditious tmp]$ 

不幸的是，Harry 的建议不起作用，它确实提取了更多信息，但还不够有用。

可以看到，得到的信息最多的就是用于签名的子密钥的密钥ID和签名的时间。这与 pgpdump（或 --list-packets）可用的数据相匹配：

bash-3.2$ pgpdump thing.txt.gpg 
Old: Compressed Data Packet(tag 8)
    Comp alg - ZLIB <RFC1950>(comp 2)
Old: One-Pass Signature Packet(tag 4)(13 bytes)
    New version(3)
    Sig type - Signature of a binary document(0x00).
    Hash alg - SHA512(hash 10)
    Pub alg - RSA Encrypt or Sign(pub 1)
    Key ID - 0x7FF2D37135C7553C
    Next packet - other than one pass signature
Old: Literal Data Packet(tag 11)(24 bytes)
    Format - binary
    Filename - thing.txt
    File modified time - Thu Sep 26 06:51:39 EST 2013
    Literal - ...
Old: Signature Packet(tag 2)(412 bytes)
    Ver 4 - new
    Sig type - Signature of a binary document(0x00).
    Pub alg - RSA Encrypt or Sign(pub 1)
    Hash alg - SHA512(hash 10)
    Hashed Sub: signature creation time(sub 2)(4 bytes)
        Time - Thu Sep 26 06:51:39 EST 2013
    Sub: issuer key ID(sub 16)(8 bytes)
        Key ID - 0x7FF2D37135C7553C
    Hash left 2 bytes - f0 97 
    RSA m^d mod n(3066 bits) - ...
        -> PKCS-1
bash-3.2$ 

如你所见，它提供了哈希算法，密钥类型的详细信息（我的签名密钥是一个 3072 位的 RSA 子密钥和子密钥的密钥 ID，但没有什么可以识别主密钥。这些信息只是当您拥有公钥并验证签名时显示。

然后我在该系统上导入了我的公钥并再次尝试：

[ben@seditious tmp]$ gpg -v --verify thing.txt.gpg 
gpg: original file name='thing.txt'
gpg: Signature made Thu 26 Sep 2013 06:51:39 AM EST using RSA key ID 35C7553C
gpg: using subkey 35C7553C instead of primary key 73590E5D
gpg: using PGP trust model
gpg: Good signature from "Ben M <ben@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg:                 aka "Ben M (backup email address) <benm@REDACTED>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: DB47 24E6 FA42 86C9 2B4E  55C4 321E 4E23 7359 0E5D
     Subkey fingerprint: B7F0 FE75 9387 430D D0C5  8BDB 7FF2 D371 35C7 553C
gpg: binary signature, digest algorithm SHA512
[ben@seditious tmp]$ 

现在它能够识别键并将其与主键匹配。但是，可以像这样减少这些警告的性质：

[ben@seditious tmp]$ gpg -v --verify --trust-model always thing.txt.gpg 
gpg: original file name='thing.txt'
gpg: Signature made Thu 26 Sep 2013 06:51:39 AM EST using RSA key ID 35C7553C
gpg: using subkey 35C7553C instead of primary key 73590E5D
gpg: Good signature from "Ben M <ben@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg:                 aka "Ben M (backup email address) <benm@REDACTED>"
gpg: WARNING: Using untrusted key!
gpg: binary signature, digest algorithm SHA512
[ben@seditious tmp]$ 

仍然有一个警告说它是一个不受信任的密钥，但不是很大，并且删除冗长只会将其减少为：

[ben@seditious tmp]$ gpg --verify --trust-model always thing.txt.gpg 
gpg: Signature made Thu 26 Sep 2013 06:51:39 AM EST using RSA key ID 35C7553C
gpg: Good signature from "Ben M <ben@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg:                 aka "Ben M (backup email address) <benm@REDACTED>"
gpg: WARNING: Using untrusted key!
[ben@seditious tmp]$ 

验证阶段需要公钥，因为它用于将签名者生成的数据与其私钥进行匹配。简单来说，它可以被认为是加密的补充，其中需要私钥来解密加密为公钥的数据。

注意：我在这个例子中稍微调整了 UID，但是每个获得该密钥的人都会看到它们的真实情况。否则输出是直接复制和粘贴。

编辑：如果您拥有非 ASCII 装甲格式（即 .gpg 文件而不是 .asc 文件），您可以像密钥环一样直接调用公钥文件。即便如此，您仍然需要公钥。要做到这一点，命令是这样的：

[ben@seditious ~]$ gpg -v --no-default-keyring --keyring /tmp/mykey.gpg --verify /tmp/thing.txt.gpg 
gpg: original file name='thing.txt'
gpg: Signature made Thu 26 Sep 2013 06:51:39 AM EST using RSA key ID 35C7553C
gpg: using subkey 35C7553C instead of primary key 73590E5D
gpg: using PGP trust model
gpg: Good signature from "Ben M <ben@REDACTED>"
gpg:                 aka "Ben M (backup email address) <benm@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg:                 aka "Ben M <ben.m@REDACTED>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: DB47 24E6 FA42 86C9 2B4E  55C4 321E 4E23 7359 0E5D
     Subkey fingerprint: B7F0 FE75 9387 430D D0C5  8BDB 7FF2 D371 35C7 553C
gpg: binary signature, digest algorithm SHA512
[ben@seditious ~]$