Created a 2G file for test purposes.

fallocate -l 2G test.img

Tried to sign it.

signify-openbsd -S -s ./keyname.sec -m ./test.img -x ./test.img.sig

result:

signify-openbsd: msg too large in ./test.img

Could you please add support for signing arbitrarily large files?

Minisign gives me an error when I try to use it to verify a signature made by Signify. From the docs it seems like this is intended to work.

$ echo VGhpcyBpcyBhIHRlc3QgbWVzc2FnZS4K | base64 --decode > message.txt
$ signify -G -p sign.pub -s sign.sec
passphrase: (z)
confirm passphrase: (z)
$ cat sign.sec
untrusted comment: signify secret key
RWRCSwAAACrVwvFk3aEyZFmPQ3kkX8eVAXYt/DvCvS3JD4o2QgWw5dPT1GwM0/u9lgqB03XQqr5yJJx9f49kmX5vd6NBBHa0rk4e9XC8mVs6Q1jWMCmO6aQTjcLOHFhLr9Vxc+W+NSw=
$ signify -S -s sign.sec -m message.txt
passphrase: (z)
$ cat message.txt.sig
untrusted comment: verify with sign.pub
RWTJD4o2QgWw5Yl4xS5JBgxC4Zv+KnDXYfDJzpE6LU/FZbs5vHq2kVJ5E7ruNvUUL+sg1/OSOvnI6N6A57wpc2VrWwujA/m8mwU=
$ ls
message.txt     message.txt.sig sign.pub        sign.sec
$ signify -V -p sign.pub -m message.txt -x message.txt.sig
Signature Verified
$ minisign -V -p sign.pub -m message.txt -x message.txt.sig
message.txt.sig: Undefined error: 0
$ minisign -v
minisign 0.8

The other way around works okay. Signify can verify minisign signatures:

$ rm sign.pub sign.sec
$ minisign -G -p sign.pub -s sign.sec
Please enter a password to protect the secret key.

Password: (z)
Password (one more time):
Deriving a key from the password in order to encrypt the secret key... done

The secret key was saved as sign.sec - Keep it secret!
The public key was saved as sign.pub - That one can be public.

Files signed using this key pair can be verified with the following command:

minisign -Vm <file> -P RWSaFhePk+tC9vTTi+yeIO4Wl6ncKXi9+ic+Rj0nohuwNC/ZWZLgBoEx
$ cat sign.sec
untrusted comment: minisign encrypted secret key
RWRTY0Iy8Ih0p+rQl2n6xucscPJOdSK48PM+Un6uFrhB74CZR/oAAAACAAAAAAAAAEAAAAAAXEf+5XzHb5GZ0vHG9ToGyICcgqEyB6kj1FAX0o/rO5o6bjIPvf3dJYo9qbOUYhWCv+56u9rnEywSGLzL9+XFmp3B2wwh14cw2+VsVe6saQG/fjrI2/C3vjUbpX1pKzGhGO391w6IawQ=
$ minisign -S -s sign.sec -m message.txt
Password: (z)
Deriving a key from the password and decrypting the secret key... done
$ cat message.txt.minisig
untrusted comment: signature from minisign secret key
RWSaFhePk+tC9snG7mzd/58ED3RdUFmO3KkyR5K8Vx/4WJCkRqHKBtUAVe4zSkoG2TgDGAImnjKBmHChbbjAxoD+TaY81Owx6AE=
trusted comment: timestamp:1563858228   file:message.txt
D1HGUOIL0Qc9OqibpK7QwMO3crzhoUdaur25n1eyMBL2q4r0loThMZycevcN1bMOg61h6cA5+PuBY8kE6MxFAw==
$ minisign -V -p sign.pub -m message.txt -x message.txt.minisig
Signature and comment signature verified
Trusted comment: timestamp:1563858228   file:message.txt
$ signify -V -p sign.pub -m message.txt -x message.txt.minisig
Signature Verified

Just in case this is somehow system-specific, I'm on MacOS with minisign and signify installed from Homebrew.

$ brew info signify-osx
signify-osx: stable 1.4 (bottled), HEAD
Cryptographically sign and verify files
https://man.openbsd.org/signify.1
/usr/local/Cellar/signify-osx/1.4 (6 files, 174.8KB) *
  Poured from bottle on 2019-07-22 at 14:46:59
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/signify-osx.rb
==> Options
--HEAD
    Install HEAD version
==> Analytics
install: 28 (30 days), 59 (90 days), 221 (365 days)
install_on_request: 28 (30 days), 58 (90 days), 208 (365 days)
build_error: 0 (30 days)
$ brew info minisign
minisign: stable 0.8 (bottled)
Sign files & verify signatures. Works with signify in OpenBSD
https://jedisct1.github.io/minisign/
/usr/local/Cellar/minisign/0.8 (6 files, 38.1KB) *
  Poured from bottle on 2019-07-22 at 13:40:52
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/minisign.rb
==> Dependencies
Build: cmake ✔
Required: libsodium ✔
==> Analytics
install: 85 (30 days), 172 (90 days), 644 (365 days)
install_on_request: 63 (30 days), 116 (90 days), 420 (365 days)
build_error: 0 (30 days)