f6c013dfa1
A signature attached to a signed commit, and the contents of the commit that merged a signed tag, are both recorded as a value of an object header field as a multi-line value, and are subject to the formatting convention for multi-line values in the headers, with a leading SP signaling that the rest of the line is a continuation of the previous line. Most notably, an empty line in such a multi-line value would result in a line with a sole SP on it. Examples in the signature-format technical documentation include a few of these cases but we did not show these otherwise invisible SPs in the example. These trailing spaces cannot be seen on display or on paper, and forces the readers to look for them in their editors or pagers, even if we added them to the document. Extend the overview section to explain the multi-line value formatting and highlight these otherwise invisible SPs by inventing the "a dollar-sign at the end of line that appears after SP merely signals that there is a SP there, and the dollar-sign itself does not appear in the real file" notation, inspired by "cat -e" output, to help readers to learn exactly where such "a single SP that is originally an empty line" appears in the examples. Reported-by: Rob Browning <rlb@defaultvalue.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
203 lines
7.3 KiB
Plaintext
203 lines
7.3 KiB
Plaintext
Git signature format
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====================
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== Overview
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Git uses cryptographic signatures in various places, currently objects (tags,
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commits, mergetags) and transactions (pushes). In every case, the command which
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is about to create an object or transaction determines a payload from that,
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calls gpg to obtain a detached signature for the payload (`gpg -bsa`) and
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embeds the signature into the object or transaction.
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Signatures always begin with `-----BEGIN PGP SIGNATURE-----`
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and end with `-----END PGP SIGNATURE-----`, unless gpg is told to
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produce RFC1991 signatures which use `MESSAGE` instead of `SIGNATURE`.
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Signatures sometimes appear as a part of the normal payload
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(e.g. a signed tag has the signature block appended after the payload
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that the signature applies to), and sometimes appear in the value of
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an object header (e.g. a merge commit that merged a signed tag would
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have the entire tag contents on its "mergetag" header). In the case
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of the latter, the usual multi-line formatting rule for object
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headers applies. I.e. the second and subsequent lines are prefixed
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with a SP to signal that the line is continued from the previous
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line.
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This is even true for an originally empty line. In the following
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examples, the end of line that ends with a whitespace letter is
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highlighted with a `$` sign; if you are trying to recreate these
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example by hand, do not cut and paste them---they are there
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primarily to highlight extra whitespace at the end of some lines.
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The signed payload and the way the signature is embedded depends
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on the type of the object resp. transaction.
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== Tag signatures
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- created by: `git tag -s`
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- payload: annotated tag object
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- embedding: append the signature to the unsigned tag object
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- example: tag `signedtag` with subject `signed tag`
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----
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object 04b871796dc0420f8e7561a895b52484b701d51a
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type commit
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tag signedtag
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tagger C O Mitter <committer@example.com> 1465981006 +0000
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signed tag
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signed tag message body
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-----BEGIN PGP SIGNATURE-----
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Version: GnuPG v1
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iQEcBAABAgAGBQJXYRhOAAoJEGEJLoW3InGJklkIAIcnhL7RwEb/+QeX9enkXhxn
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rxfdqrvWd1K80sl2TOt8Bg/NYwrUBw/RWJ+sg/hhHp4WtvE1HDGHlkEz3y11Lkuh
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8tSxS3qKTxXUGozyPGuE90sJfExhZlW4knIQ1wt/yWqM+33E9pN4hzPqLwyrdods
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q8FWEqPPUbSJXoMbRPw04S5jrLtZSsUWbRYjmJCHzlhSfFWW4eFd37uquIaLUBS0
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rkC3Jrx7420jkIpgFcTI2s60uhSQLzgcCwdA2ukSYIRnjg/zDkj8+3h/GaROJ72x
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lZyI6HWixKJkWw8lE9aAOD9TmTW9sFJwcVAzmAuFX2kUreDUKMZduGcoRYGpD7E=
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=jpXa
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-----END PGP SIGNATURE-----
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----
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- verify with: `git verify-tag [-v]` or `git tag -v`
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----
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gpg: Signature made Wed Jun 15 10:56:46 2016 CEST using RSA key ID B7227189
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gpg: Good signature from "Eris Discordia <discord@example.net>"
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
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object 04b871796dc0420f8e7561a895b52484b701d51a
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type commit
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tag signedtag
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tagger C O Mitter <committer@example.com> 1465981006 +0000
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signed tag
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signed tag message body
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----
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== Commit signatures
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- created by: `git commit -S`
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- payload: commit object
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- embedding: header entry `gpgsig`
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(content is preceded by a space)
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- example: commit with subject `signed commit`
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----
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tree eebfed94e75e7760540d1485c740902590a00332
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parent 04b871796dc0420f8e7561a895b52484b701d51a
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author A U Thor <author@example.com> 1465981137 +0000
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committer C O Mitter <committer@example.com> 1465981137 +0000
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gpgsig -----BEGIN PGP SIGNATURE-----
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Version: GnuPG v1
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$
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iQEcBAABAgAGBQJXYRjRAAoJEGEJLoW3InGJ3IwIAIY4SA6GxY3BjL60YyvsJPh/
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HRCJwH+w7wt3Yc/9/bW2F+gF72kdHOOs2jfv+OZhq0q4OAN6fvVSczISY/82LpS7
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DVdMQj2/YcHDT4xrDNBnXnviDO9G7am/9OE77kEbXrp7QPxvhjkicHNwy2rEflAA
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zn075rtEERDHr8nRYiDh8eVrefSO7D+bdQ7gv+7GsYMsd2auJWi1dHOSfTr9HIF4
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HJhWXT9d2f8W+diRYXGh4X0wYiGg6na/soXc+vdtDYBzIxanRqjg8jCAeo1eOTk1
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EdTwhcTZlI0x5pvJ3H0+4hA2jtldVtmPM4OTB0cTrEWBad7XV6YgiyuII73Ve3I=
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=jKHM
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-----END PGP SIGNATURE-----
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signed commit
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signed commit message body
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----
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- verify with: `git verify-commit [-v]` (or `git show --show-signature`)
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----
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gpg: Signature made Wed Jun 15 10:58:57 2016 CEST using RSA key ID B7227189
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gpg: Good signature from "Eris Discordia <discord@example.net>"
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
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tree eebfed94e75e7760540d1485c740902590a00332
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parent 04b871796dc0420f8e7561a895b52484b701d51a
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author A U Thor <author@example.com> 1465981137 +0000
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committer C O Mitter <committer@example.com> 1465981137 +0000
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signed commit
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signed commit message body
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----
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== Mergetag signatures
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- created by: `git merge` on signed tag
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- payload/embedding: the whole signed tag object is embedded into
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the (merge) commit object as header entry `mergetag`
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- example: merge of the signed tag `signedtag` as above
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----
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tree c7b1cff039a93f3600a1d18b82d26688668c7dea
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parent c33429be94b5f2d3ee9b0adad223f877f174b05d
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parent 04b871796dc0420f8e7561a895b52484b701d51a
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author A U Thor <author@example.com> 1465982009 +0000
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committer C O Mitter <committer@example.com> 1465982009 +0000
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mergetag object 04b871796dc0420f8e7561a895b52484b701d51a
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type commit
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tag signedtag
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tagger C O Mitter <committer@example.com> 1465981006 +0000
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$
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signed tag
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$
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signed tag message body
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-----BEGIN PGP SIGNATURE-----
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Version: GnuPG v1
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$
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iQEcBAABAgAGBQJXYRhOAAoJEGEJLoW3InGJklkIAIcnhL7RwEb/+QeX9enkXhxn
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rxfdqrvWd1K80sl2TOt8Bg/NYwrUBw/RWJ+sg/hhHp4WtvE1HDGHlkEz3y11Lkuh
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8tSxS3qKTxXUGozyPGuE90sJfExhZlW4knIQ1wt/yWqM+33E9pN4hzPqLwyrdods
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q8FWEqPPUbSJXoMbRPw04S5jrLtZSsUWbRYjmJCHzlhSfFWW4eFd37uquIaLUBS0
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rkC3Jrx7420jkIpgFcTI2s60uhSQLzgcCwdA2ukSYIRnjg/zDkj8+3h/GaROJ72x
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lZyI6HWixKJkWw8lE9aAOD9TmTW9sFJwcVAzmAuFX2kUreDUKMZduGcoRYGpD7E=
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=jpXa
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-----END PGP SIGNATURE-----
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Merge tag 'signedtag' into downstream
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signed tag
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signed tag message body
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# gpg: Signature made Wed Jun 15 08:56:46 2016 UTC using RSA key ID B7227189
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# gpg: Good signature from "Eris Discordia <discord@example.net>"
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# gpg: WARNING: This key is not certified with a trusted signature!
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# gpg: There is no indication that the signature belongs to the owner.
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# Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
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----
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- verify with: verification is embedded in merge commit message by default,
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alternatively with `git show --show-signature`:
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----
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commit 9863f0c76ff78712b6800e199a46aa56afbcbd49
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merged tag 'signedtag'
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gpg: Signature made Wed Jun 15 10:56:46 2016 CEST using RSA key ID B7227189
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gpg: Good signature from "Eris Discordia <discord@example.net>"
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
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Merge: c33429b 04b8717
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Author: A U Thor <author@example.com>
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Date: Wed Jun 15 09:13:29 2016 +0000
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Merge tag 'signedtag' into downstream
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signed tag
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signed tag message body
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# gpg: Signature made Wed Jun 15 08:56:46 2016 UTC using RSA key ID B7227189
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# gpg: Good signature from "Eris Discordia <discord@example.net>"
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# gpg: WARNING: This key is not certified with a trusted signature!
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# gpg: There is no indication that the signature belongs to the owner.
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# Primary key fingerprint: D4BE 2231 1AD3 131E 5EDA 29A4 6109 2E85 B722 7189
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----
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