如何在不使用密钥服务器的情况下从OpenPGP智能卡获取公钥？

Question

如何在不使用密钥服务器的情况下从OpenPGP智能卡获取公钥？

securitypublic-key-encryptiongnupg

17

我正在处理这样一个用例，其中OpenPGP被用于在智能卡（Yubikey）上生成公钥对。

然后将智能卡发送给用户。为了在本地模拟这个过程，执行以下步骤：

在智能卡上生成密钥
删除GnuPG主目录
访问智能卡以重新生成GnuPG主目录

问题是，在执行上述步骤之后，我无法测试加密文件，因为公钥似乎已经丢失。 fetch 似乎不起作用。

此时，我不想在任何在线服务器上共享公钥。是否有办法在删除密钥环之后从智能卡检索公钥？

以下是正在执行的步骤：

$ gpg --card-edit                                                                                                                                                       

Reader ...........: 1050:0404:X:0
Application ID ...: D2760001240102010006046314290000
Version ..........: 2.1
Manufacturer .....: Yubico
Serial number ....: 04631429
Name of cardholder: sm sm
Language prefs ...: en
Sex ..............: unspecified
URL of public key : [not set]
Login data .......: sm
Signature PIN ....: not forced
Key attributes ...: rsa4096 rsa4096 rsa4096
Max. PIN lengths .: 127 127 127
PIN retry counter : 3 0 3
Signature counter : 0
Signature key ....: 54D4 E469 7056 B390 AE72  CAA1 A507 3320 7876 0302
      created ....: 2017-10-11 13:16:52
Encryption key....: ADA3 2D7F 8D66 4F34 C04A  457C DFEB E3E4 A8F1 8611
      created ....: 2017-10-11 11:14:18
Authentication key: 18B9 7AB4 0723 46F4 C23A  3DD7 E5C0 6A93 049E F6A8
      created ....: 2017-10-11 11:14:18
General key info..: [none]

gpg/card> admin
Admin commands are allowed

gpg/card> generate
Make off-card backup of encryption key? (Y/n) n

gpg: Note: keys are already stored on the card!

Replace existing keys? (y/N) y
What keysize do you want for the Signature key? (4096) 
What keysize do you want for the Encryption key? (4096) 
What keysize do you want for the Authentication key? (4096) 
Key is valid for? (0) 0
Is this correct? (y/N) y
Real name: john doe
Email address: john.doe@foobar.com
Comment: 
You selected this USER-ID:
    "john doe <<john.doe@foobar.com>"

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o

gpg: /home/xxx/.gnupg/trustdb.gpg: trustdb created
gpg: key 6825CB0EBDA94110 marked as ultimately trusted
gpg: directory '/home/xxx/.gnupg/openpgp-revocs.d' created
gpg: revocation certificate stored as '/home/xxx/.gnupg/openpgp-revocs.d/6858F119E93FB74BB561DE556825CB0EBDA94110.rev'
public and secret key created and signed.


gpg/card> list

Reader ...........: 1050:0404:X:0
Application ID ...: D2760001240102010006046314290000
Version ..........: 2.1
Manufacturer .....: Yubico
Serial number ....: 04631429
Name of cardholder: sm sm
Language prefs ...: en
Sex ..............: unspecified
URL of public key : [not set]
Login data .......: sm
Signature PIN ....: not forced
Key attributes ...: rsa4096 rsa4096 rsa4096
Max. PIN lengths .: 127 127 127
PIN retry counter : 3 0 3
Signature counter : 4
Signature key ....: 6858 F119 E93F B74B B561  DE55 6825 CB0E BDA9 4110
      created ....: 2017-10-11 13:18:11
Encryption key....: BE05 7FDF 9ACD 05F0 B75A  570F 4711 4B69 A622 C1DC
      created ....: 2017-10-11 13:18:11
Authentication key: 7275 2C47 B1EF BFB5 1E6D  0E65 31C7 7DBE 2D22 7E32
      created ....: 2017-10-11 13:18:11
General key info..: pub  rsa4096/6825CB0EBDA94110 2017-10-11     john doe <<john.doe@foobar.com>
sec>  rsa4096/6825CB0EBDA94110  created: 2017-10-11  expires: never     
                                card-no: 0006 04631429
ssb>  rsa4096/31C77DBE2D227E32  created: 2017-10-11  expires: never     
                                card-no: 0006 04631429
ssb>  rsa4096/47114B69A622C1DC  created: 2017-10-11  expires: never     
                                card-no: 0006 04631429

gpg/card> quit

$ rm -rf .gnupg/

$ gpg --card-status                                                                                                                                                     
gpg: directory '/home/smalatho/.gnupg' created
gpg: new configuration file '/home/smalatho/.gnupg/dirmngr.conf' created
gpg: new configuration file '/home/smalatho/.gnupg/gpg.conf' created
gpg: keybox '/home/smalatho/.gnupg/pubring.kbx' created
Reader ...........: 1050:0404:X:0
Application ID ...: D2760001240102010006046314290000
Version ..........: 2.1
Manufacturer .....: Yubico
Serial number ....: 04631429
Name of cardholder: sm sm
Language prefs ...: en
Sex ..............: unspecified
URL of public key : [not set]
Login data .......: sm
Signature PIN ....: not forced
Key attributes ...: rsa4096 rsa4096 rsa4096
Max. PIN lengths .: 127 127 127
PIN retry counter : 3 0 3
Signature counter : 4
Signature key ....: 6858 F119 E93F B74B B561  DE55 6825 CB0E BDA9 4110
      created ....: 2017-10-11 13:18:11
Encryption key....: BE05 7FDF 9ACD 05F0 B75A  570F 4711 4B69 A622 C1DC
      created ....: 2017-10-11 13:18:11
Authentication key: 7275 2C47 B1EF BFB5 1E6D  0E65 31C7 7DBE 2D22 7E32
      created ....: 2017-10-11 13:18:11
General key info..: [none]

- Stelios

3个回答

3

在删除GNUPGHOME目录之前，需要用户手动导出公钥，然后将公钥重新导入智能卡。

$ gpg --armor --export j.doe@example.com > public.asc
$ rm -rf ~/.gnupg
$ gpg --import public.asc

- Stelios

我不明白：要导出公钥（以便稍后再次导入），您必须拥有它。但是当您拥有它时，您的命令有什么意义呢？ - U. Windl

1

根据GnuPG的维护者所说，仅使用来自卡片的信息重建公钥在技术上是可能的，但并不容易。

However, if you really lost the public key and you need it back, it is possible to re-create the public key with the same fingerprint. There is no code for this, you need to hack the source.

What you need is the creation timestamp and the public key parameters from the card. You can gather this information using
  $ gpg-connect-agent
  > scd learn --force
  S SERIALNO D276000124010101000100xxxxxxxxxx  0
  S APPTYPE OPENPGP
[...]
  S KEY-TIME 1 1136130759
  S KEY-TIME 2 1136132140
  S KEY-TIME 3 1136131786
[...]
  OK
  > /decode
  > /hex
  > scd readkey OPENPGP.1
  D[0000]  28 31 30 3A 70 75 62 6C  69 63 2D 6B 65 79 28 33   (10:public-key(3
  D[0010]  3A 72 73 61 28 31 3A 6E  31 32 39 3A 00 D0 99 19   :rsa(1:n129:....
[...]
  OK
Take the creation time from the KEY-TIME lines. I used /decode and /hex above only for readability. You should use
  > /datafile out
  > scd readkey OPENPGP.1
  OK
  > /bye
instead which writes the s-expression with the public key to the file out. The Libgcrypt functions take those s-expressions as arguments. Now you need to feed it to gpg to create the public key part and the self-signatures.

- Richard Hansen

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- Jens Erat · Accepted Answer

10

OpenPGP智能卡没有存储足够的信息来重建完整的OpenPGP公钥。你必须单独导入公钥--在密钥服务器上共享它是一个解决方案，但你也可以使用gpg --export导出密钥，然后再次使用gpg --import进行测试。

- Jens Erat

1

我猜密钥服务器存储的信息和本地公钥环相同？ - Stelios

2

实际上，密钥服务器只提供未经验证的密钥，并基于密钥ID或指纹（长密钥ID和指纹定义了一个给定密钥，具有非常低的碰撞几率）或用户ID进行查找（根本没有验证，只需在密钥服务器网络中搜索“president@whitehouse.gov”）。从这个意义上讲，上传到存储库的密钥是更强的概念，因为它允许像上面讨论的那样的“第一次使用信任”。无论您以哪种方式检索密钥（从存储库，从密钥服务器），您仍然需要验证密钥。 - Jens Erat

有没有一些可以从OpenPGP智能卡中提取公钥的部分信息？如何提取它？ - pts

2

密钥的指纹存储在卡片上，可以用作从密钥服务器检索公钥的参考（如果已上传到服务器）。 - Jens Erat

非常感谢。当我换到新笔记本电脑时，我已经寻找很长时间来解决这个问题，我的提交签名出现了故障！ - DeejUK

我以为私钥中也包含公钥？也许它不包括用户ID和签名，但是相对容易添加。不过，从密钥服务器或备份中获取数据更加容易。 - U. Windl