Generating a base64 encoded SHA512 digest for a file (or set of files)

Question

The BlackBerry WebWorks SDK for Tablet OS build tool generates an archive that contains the files and a MANIFEST.MF with entry for each file and a base64 encoded SHA512 digest. However, there is a bug that too many files in the build will cause a build failure. I am trying to figure out how to generate that same information myself.

The example below comes from the MANIFEST.MF and it contains the filename and digest. However, the base64 variant uses _ instead of / and - instead of + and has no trailing == for padding.

Archive-Asset-Name: air/XX/IMG_0999.jpg
Archive-Asset-SHA-512-Digest: YI_KXWjpJwwsi5MDQPeBQc9SVi-bH6zYq5PgBD3jQiqHu-r-5Hv8A0yh_y5j2T9MpYZ5TVMW4JXHSXNYmpV1tA

I running Windows 7, but have GIT installed so I have MINGW32 as a bash shell. I found this piped combination of openssl and tr commands but it seems a bit of a kludge.

openssl dgst -sha512 -binary IMG_0999.gif | openssl enc -base64 | tr '+' '-' | tr '/' '_' | tr -d '=' | tr -d '\n'

Is there a better way to generate this digest?

Eventually, I will have to do for all the images in a directory tree. I was hoping for a script solution instead of having to write a program. A second question is how to generate that manifest syntax for all files in a directory (recursively). Would this be a bash shell script encompassing the above command? Any pointers here are appreciated since I haven't written a shell script before.

Answer 1

Dennis Williamson's solution got me going but the tr version (2.0) that is installed did like that multiple character syntax. Also, the xargs version (4.1) didn't like the -I option. However, it got me started and that is what matters. Here is what I ended up with:

find . -type f -name '*.gif' -print0 | xargs -0 --replace=% sh -c 'echo -e "Archive-Asset-Name: %\nArchive-Asset-SHA-512-Digest: `openssl dgst -sha512 -binary % | openssl enc -base64 | tr "+" "-" | tr "/" "_" | tr -d "=" | tr -d "\n"`\n"'

and that generates the following (images names changed to protect the innocent)

Archive-Asset-Name: ./IMG_0001.gif
Archive-Asset-SHA-512-Digest: AsgQnXYxj07qy-DTlzqYEv3v1UNqbr1sp5kVz0PE8FYwD-q_0VM20Wyci3xunJwdqy59MbyIX1GGtSmhuETUHQ

Archive-Asset-Name: ./IMG_0032.gif
Archive-Asset-SHA-512-Digest: JE3lmvXxOjSpDoUjyvAp92E1T4b8AQGGJBCcBz_1AG2eoBoSRH76LHpWPEUAeXFx_kOqEaDMRGPrpYnlfcnz9g

Archive-Asset-Name: ./IMG_0003.gif
Archive-Asset-SHA-512-Digest: bJJQ-j-s9630FzUh3hP50h7gWYqJQ6o0FP37nUuSeSUmerFxBwR2X0VeTYn-h4cf7szUr4fqDfAKQLOK0gt7zA

I still need to tweak the name to not be prefixed with ./ but that is for another day.

Answer 2

You can shorten your command by combining some things:

openssl dgst -sha512 -binary IMG_0999.gif | openssl enc -base64 | tr '+/' '-_' | tr -d '=\n'

For all files in a tree, something like:

find . -type f -name '*.gif' -print0 | xargs -0 -I % sh -c 'openssl dgst -sha512 -binary "$(basename "$1")" | openssl enc -base64 | tr "+/" "-_" | tr -d "=\n" > "$1.sum"' _ $1