Provided by: signapk_8.1.0+r23-2~18.04_all 

NAME
signapk - JAR and APK signing tool
SYNOPSIS
Command line tool for signing Android ZIP/JAR/APK files:
signapk [-w] [-a alignment] [-providerClass className] publickey.x509[.pem] privatekey.pk8 [publick‐
ey2.x509[.pem] privatekey2.pk8 ...] input.jar output.jar signapk file.jar
input.jar is an existing file to sign.
DESCRIPTION
Signs ZIP files, including JARs, APKs and Over-The-Air (OTA) updates, in a way compatible with Android's
mincrypt verifier, using EC or RSA keys and SHA1 or SHA-256. The tool can additionally sign APKs using
APK Signature Scheme v2. It is the standard tool used to sign APK and JAR files distributed as part of
Android ROMs.
HISTORICAL NOTE
Prior to the KitKat (aka 4.4.2 aka android-19) release, signapk ignored the signature algorithm specified
in the certificate and always used SHA1withRSA.
Starting with JellyBean-MR2 (aka 4.3 aka android-18), the platform supports SHA256withRSA, so we use the
signature algorithm in the certificate to select which to use (SHA256withRSA or SHA1withRSA). Also in
JellyBean-MR2, EC keys are supported.
Because there are old keys still in use whose certificate actually says “MD5withRSA”, those are treated
as though they say “SHA1withRSA” for compatibility with older releases.
SEE ALSO
JAR(1)
ZIP(1)
ZIPALIGN(1)
https://source.android.com/devices/tech/ota/sign_builds.html
AUTHORS
The Android Open Source Project.
SIGNAPK(1)