[Q] Is it possible to reduce size of .apk without break signature?

1) The SHA1-Digest in the signature is based on the compressed or uncompressed files inside the apk?
2) If it is based on the uncompressed files, is it possible to decompress and recompress with 7-zip utility (always in the zip format) and then zipalign without break the signature?
3) Is there an online service or an application to verify that the signature match the files?

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