Set passphrase only for the fingerprint being used (#123)

* If fingerprint input is provided it sets only the passphrase for that key

* Update README with how to use subkeys example

README.md

@@ -120,6 +120,51 @@ jobs:
           git push
 ```
 
+### Use a subkey
+
+With the input `fingerprint`, you can specify which one of the subkeys in a GPG key you want to use for signing.
+
+```yaml
+name: import-gpg
+
+on:
+  push:
+    branches: master
+
+jobs:
+  import-gpg:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Import GPG key
+        id: import_gpg
+        uses: crazy-max/ghaction-import-gpg@v4
+        with:
+          gpg_private_key: ${{ secrets.GPG_PRIVATE_KEY }}
+          passphrase: ${{ secrets.PASSPHRASE }}
+          fingerprint: "C17D11ADF199F12A30A0910F1F80449BE0B08CB8"
+      -
+        name: List keys
+        run: gpg -K
+```
+
+For example, given this GPG key with a signing subkey:
+
+```s
+pub   ed25519 2021-09-24 [C]
+      87F257B89CE462100BEC0FFE6071D218380FDCC8
+      Keygrip = F5C3ABFAAB36B427FD98C4EDD0387E08EA1E8092
+uid           [ unknown] Joe Bar <joe@bar.foo>
+sub   ed25519 2021-09-24 [S]
+      C17D11ADF199F12A30A0910F1F80449BE0B08CB8
+      Keygrip = DEE0FC98F441519CA5DE5D79773CB29009695FEB
+```
+
+You can use the subkey with signing capability whose fingerprint is `C17D11ADF199F12A30A0910F1F80449BE0B08CB8`.
+
 ## Customizing
 
 ### inputs

__tests__/fixtures/test-key-gpg-output.txt

@@ -0,0 +1,8 @@
+tru::1:1645715610:1661267528:3:1:5
+pub:-:4096:1:7D851EB72D73BDA0:1588448672:::-:::scESC::::::23::0:
+fpr:::::::::27571A53B86AF0C799B38BA77D851EB72D73BDA0:
+grp:::::::::3E2D1142AA59E08E16B7E2C64BA6DDC773B1A627:
+uid:-::::1588448672::C1B25336F8F0F0F22BAF57137BE493ADEDA8CCAA::Joe Tester <joe@foo.bar>::::::::::0:
+sub:-:4096:1:D523BD50DD70B0BA:1588448672::::::e::::::23:
+fpr:::::::::5A282E1460C0BC419615D34DD523BD50DD70B0BA:
+grp:::::::::BA83FC8947213477F28ADC019F6564A956456163:

__tests__/fixtures/test-subkey-gpg-output.txt

@@ -0,0 +1,8 @@
+tru::1:1645715610:1661267528:3:1:5
+pub:-:256:22:6071D218380FDCC8:1632521434:::-:::cSC:::::ed25519:::0:
+fpr:::::::::87F257B89CE462100BEC0FFE6071D218380FDCC8:
+grp:::::::::F5C3ABFAAB36B427FD98C4EDD0387E08EA1E8092:
+uid:-::::1632521434::019F22ECD701BC0F6AFE686ABD2B010B812B828E::Joe Bar <joe@bar.foo>::::::::::0:
+sub:-:256:22:1F80449BE0B08CB8:1632521539::::::s:::::ed25519::
+fpr:::::::::C17D11ADF199F12A30A0910F1F80449BE0B08CB8:
+grp:::::::::DEE0FC98F441519CA5DE5D79773CB29009695FEB:

__tests__/gpg.test.ts

@@ -1,5 +1,6 @@
 import * as fs from 'fs';
 import * as gpg from '../src/gpg';
+import {parseKeygripFromGpgColonsOutput} from '../src/gpg';
 
 const userInfos = [
   {
@@ -20,6 +21,7 @@ const userInfos = [
     email: 'joe@foo.bar',
     keyID: '7D851EB72D73BDA0',
     fingerprint: '27571A53B86AF0C799B38BA77D851EB72D73BDA0',
+    fingerprints: ['27571A53B86AF0C799B38BA77D851EB72D73BDA0', '5A282E1460C0BC419615D34DD523BD50DD70B0BA'],
     keygrips: ['3E2D1142AA59E08E16B7E2C64BA6DDC773B1A627', 'BA83FC8947213477F28ADC019F6564A956456163']
   },
   {
@@ -40,6 +42,7 @@ const userInfos = [
     email: 'joe@bar.foo',
     keyID: '6071D218380FDCC8',
     fingerprint: 'C17D11ADF199F12A30A0910F1F80449BE0B08CB8',
+    fingerprints: ['87F257B89CE462100BEC0FFE6071D218380FDCC8', 'C17D11ADF199F12A30A0910F1F80449BE0B08CB8'],
     keygrips: ['F5C3ABFAAB36B427FD98C4EDD0387E08EA1E8092', 'DEE0FC98F441519CA5DE5D79773CB29009695FEB']
   }
 ];
@@ -101,6 +104,19 @@ for (let userInfo of userInfos) {
       });
     });
 
+    describe('getKeygrip', () => {
+      it('returns the keygrip for a given fingerprint', async () => {
+        await gpg.importKey(userInfo.pgp);
+        for (let [i, fingerprint] of userInfo.fingerprints.entries()) {
+          await gpg.getKeygrip(fingerprint).then(keygrip => {
+            console.log(`Fingerprint: ${fingerprint}; Index: ${i}; Keygrip: ${keygrip}`);
+            expect(keygrip.length).toEqual(userInfo.keygrips[i].length);
+            expect(keygrip).toEqual(userInfo.keygrips[i]);
+          });
+        }
+      });
+    });
+
     describe('presetPassphrase', () => {
       it('presets passphrase', async () => {
         await gpg.importKey(userInfo.pgp);
@@ -128,3 +144,29 @@ describe('killAgent', () => {
     await gpg.killAgent();
   });
 });
+
+describe('parseKeygripFromGpgColonsOutput', () => {
+  it('returns the keygrip of a given fingerprint from a GPG command output using the option: --with-colons', async () => {
+    const outputUsingTestKey = fs.readFileSync('__tests__/fixtures/test-key-gpg-output.txt', {
+      encoding: 'utf8',
+      flag: 'r'
+    });
+
+    const keygripPrimaryTestKey = parseKeygripFromGpgColonsOutput(outputUsingTestKey, '27571A53B86AF0C799B38BA77D851EB72D73BDA0');
+    expect(keygripPrimaryTestKey).toBe('3E2D1142AA59E08E16B7E2C64BA6DDC773B1A627');
+
+    const keygripSubkeyTestKey = parseKeygripFromGpgColonsOutput(outputUsingTestKey, '5A282E1460C0BC419615D34DD523BD50DD70B0BA');
+    expect(keygripSubkeyTestKey).toBe('BA83FC8947213477F28ADC019F6564A956456163');
+
+    const outputUsingTestSubkey = fs.readFileSync('__tests__/fixtures/test-subkey-gpg-output.txt', {
+      encoding: 'utf8',
+      flag: 'r'
+    });
+
+    const keygripPrimaryTestSubkey = parseKeygripFromGpgColonsOutput(outputUsingTestSubkey, '87F257B89CE462100BEC0FFE6071D218380FDCC8');
+    expect(keygripPrimaryTestSubkey).toBe('F5C3ABFAAB36B427FD98C4EDD0387E08EA1E8092');
+
+    const keygripSubkeyTestSubkey = parseKeygripFromGpgColonsOutput(outputUsingTestSubkey, 'C17D11ADF199F12A30A0910F1F80449BE0B08CB8');
+    expect(keygripSubkeyTestSubkey).toBe('DEE0FC98F441519CA5DE5D79773CB29009695FEB');
+  });
+});

src/gpg.ts

@@ -159,6 +159,39 @@ export const getKeygrips = async (fingerprint: string): Promise<Array<string>> =
     });
 };
 
+export const parseKeygripFromGpgColonsOutput = (output: string, fingerprint: string): string => {
+  let keygrip = '';
+  let fingerPrintFound = false;
+  const lines = output.replace(/\r/g, '').trim().split(/\n/g);
+
+  for (let line of lines) {
+    if (line.startsWith(`fpr:`) && line.includes(`:${fingerprint}:`)) {
+      // We reach the record with the matching fingerprint.
+      // The next keygrip record is the keygrip for this fingerprint.
+      fingerPrintFound = true;
+      continue;
+    }
+
+    if (line.startsWith('grp:') && fingerPrintFound) {
+      keygrip = line.replace(/(grp|:)/g, '').trim();
+      break;
+    }
+  }
+
+  return keygrip;
+};
+
+export const getKeygrip = async (fingerprint: string): Promise<string> => {
+  return await exec
+    .getExecOutput('gpg', ['--batch', '--with-colons', '--with-keygrip', '--list-secret-keys', fingerprint], {
+      ignoreReturnCode: true,
+      silent: true
+    })
+    .then(res => {
+      return parseKeygripFromGpgColonsOutput(res.stdout, fingerprint);
+    });
+};
+
 export const configureAgent = async (config: string): Promise<void> => {
   const gpgAgentConf = path.join(await getGnupgHome(), 'gpg-agent.conf');
   await fs.writeFile(gpgAgentConf, config, function (err) {

src/main.ts

@@ -48,7 +48,9 @@ async function run(): Promise<void> {
       });
     });
 
-    if (inputs.passphrase) {
+    if (inputs.passphrase && !inputs.fingerprint) {
+      // Set the passphrase for all subkeys
+
       core.info('Configuring GnuPG agent');
       await gpg.configureAgent(gpg.agentConfig);
 
@@ -62,6 +64,21 @@ async function run(): Promise<void> {
       });
     }
 
+    if (inputs.passphrase && inputs.fingerprint) {
+      // Set the passphrase only for the subkey specified in the input `fingerprint`
+
+      core.info('Configuring GnuPG agent');
+      await gpg.configureAgent(gpg.agentConfig);
+
+      await core.group(`Getting keygrip for fingerprint`, async () => {
+        const keygrip = await gpg.getKeygrip(fingerprint);
+        core.info(`Presetting passphrase for key ${fingerprint} with keygrip ${keygrip}`);
+        await gpg.presetPassphrase(keygrip, inputs.passphrase).then(stdout => {
+          core.debug(stdout);
+        });
+      });
+    }
+
     await core.group(`Setting outputs`, async () => {
       core.info(`fingerprint=${fingerprint}`);
       context.setOutput('fingerprint', fingerprint);