Haskell GPGME much slower at signing than GPG

Question

My program uses GPG for signing files. I'm using GPGME in Haskell and the issue is that it is about 16 times slower than using GPG from the command line. Here is an example:

Haskell code:

module Main where

import qualified Data.ByteString as B
import qualified Crypto.Gpgme as Gpg

main :: IO ()
main = do
    fileContents <- B.readFile "randomfile"
    eitherSigned <- sign fileContents
    case eitherSigned of
        Left err -> print err
        Right signed ->
            B.writeFile "signedfile" signed

sign :: B.ByteString -> IO (Either [Gpg.InvalidKey] B.ByteString)
sign bs =
    let
        sign' :: Gpg.Ctx -> IO (Either [Gpg.InvalidKey] Gpg.Plain)    
        sign' ctx = Gpg.sign ctx [] Gpg.Normal bs
    in
        Gpg.withCtx "/home/t/.gnupg" "C" Gpg.OpenPGP sign'

I generate a junk 10MB file with

$ dd if=/dev/zero of=randomfile bs=10000000 count=1

I sign it with GPG from the command line:

$ time gpg -s randomfile

and get

gpg -s randomfile  0.14s user 0.00s system 99% cpu 0.136 total

I sign it with my Haskell program with

$ time stack exec hasksign

and get

stack exec hasksign  0.27s user 0.07s system 14% cpu 2.239 total

I tried running the Haskell code again with profiling on and got this result:

       hasksign +RTS -p -RTS randomfile

    total time  =        2.21 secs   (2208 ticks @ 1000 us, 1 processor)
    total alloc = 115,627,312 bytes  (excludes profiling overheads)

COST CENTRE        MODULE                SRC                                           %time %alloc

newCtx             Crypto.Gpgme.Ctx      src/Crypto/Gpgme/Ctx.hs:(21,1)-(51,21)         77.0    0.0
signIntern         Crypto.Gpgme.Crypto   src/Crypto/Gpgme/Crypto.hs:(310,1)-(354,14)    20.4    8.6
collectResult.go.\ Crypto.Gpgme.Internal src/Crypto/Gpgme/Internal.hs:(29,21)-(34,46)    2.1   81.9
main               Main                  src/Main.hs:(7,1)-(13,43)                       0.1    8.7

I have looked in the newCtx function where the time is spent but it is not clear to me what is costing so much.