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Julian
Julian

Posted on • Updated on

Sign your git commits with tortoise git on windows

#git #sign #tortoisegit #windows

after reading this nice article from agrinman about spoofing a git commit, i decided i will have a look on how to sign a git commit.

it is a little bit more complicated than i thought but its still an quite easy task.

first generate a keypair (the --allow-freeform-uid is to overcome the Name must be at least 5 characters long error):

λ gpg --full-generate-key --allow-freeform-uid
gpg (GnuPG) 2.2.8; Copyright (C) 2018 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Please select what kind of key you want:
   (1) RSA and RSA (default)
   (2) DSA and Elgamal
   (3) DSA (sign only)
   (4) RSA (sign only)
Your selection? 1
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
         0 = key does not expire
      <n>  = key expires in n days
      <n>w = key expires in n weeks
      <n>m = key expires in n months
      <n>y = key expires in n years
Key is valid for? (0) 5y
Key expires at 08/09/23 18:32:52 W. Europe Daylight Time
Is this correct? (y/N) y

GnuPG needs to construct a user ID to identify your key.

Real name: devto-example
Email address: devto@example.com
Comment:
You selected this USER-ID:
    "devto-example <devto@example.com>"

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
gpg: key 8493DA39DD68724D marked as ultimately trusted
gpg: revocation certificate stored as '<REMOVED>'
public and secret key created and signed.

pub   rsa4096 2018-08-10 [SC] [expires: 2023-08-09]
      F0FB9F40A82A7F2502B652348493DA39DD68724D
uid                      devto-example <devto@example.com>
sub   rsa4096 2018-08-10 [E] [expires: 2023-08-09]
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export your public key

λ gpg --armor --export devto@example.com
-----BEGIN PGP PUBLIC KEY BLOCK-----
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=sdjc
-----END PGP PUBLIC KEY BLOCK-----
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and add it to https://gitlab.com/profile/gpg_keys and https://github.com/settings/gpg/new

then you have to configure git to use the key by adding the key id to the git config.

to get the key id run:

λ gpg --list-keys --keyid-format LONG devto@example.com
pub   rsa4096/8493DA39DD68724D 2018-08-10 [SC] [expires: 2023-08-09]
      F0FB9F40A82A7F2502B652348493DA39DD68724D
uid                 [ultimate] devto-example <devto@example.com>
sub   rsa4096/75928CD4BDEAE0D7 2018-08-10 [E] [expires: 2023-08-09]
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the sort version of the id is the part after pub rsa4096/ -> 8493DA39DD68724D and the long version is in the 2nd line F0FB9F40A82A7F2502B652348493DA39DD68724D because of key collisions i would recommend that you use the long key format.

now add/merge the following to your (global) .gitconfig

[user]
    signingkey = F0FB9F40A82A7F2502B652348493DA39DD68724D

[commit]
    gpgsign = true
[gpg]
    program = "C:/Program Files (x86)/GNU/GnuPG/gpg2.exe"
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you need to have gpg installed and adapt the program path according your install path. the signing key is your long key id. to auto sign your commits add commit.gpgsign=true.

now if you do a commit, the commit will be signed. you can easily verify that:

λ git verify-commit HEAD
gpg: Signature made 08/10/18 19:37:21 W. Europe Daylight Time
gpg:                using RSA key F0FB9F40A82A7F2502B652348493DA39DD68724D
gpg: Good signature from "devto-example<devto@example.com>" [ultimate]
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or

git log --show-signature
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