diff --git a/citadel-image/src/build.rs b/citadel-image/src/build.rs
index 3218c4d..fa4418e 100644
--- a/citadel-image/src/build.rs
+++ b/citadel-image/src/build.rs
@@ -4,7 +4,7 @@ use std::fs::{self,File};
 use std::io::{self,Write};
 
 use failure::ResultExt;
-use libcitadel::{Result,ImageHeader,util,verity};
+use libcitadel::{Result,ImageHeader,verity,util,devkeys};
 
 use BuildConfig;
 
@@ -85,7 +85,10 @@ impl UpdateBuilder {
     }
 
     fn calculate_shasum(&mut self) -> Result<()> {
-        let shasum = util::sha256(&self.target)?;
+        let output = util::exec_cmdline_with_output("sha256sum", format!("{}", self.target.display()))
+            .context(format!("failed to calculate sha256 on {}", self.target.display()))?;
+        let v: Vec<&str> = output.split_whitespace().collect();
+        let shasum = v[0].trim().to_owned();
         info!("Sha256 of image data is {}", shasum);
         self.shasum = Some(shasum);
         Ok(())
@@ -97,7 +100,6 @@ impl UpdateBuilder {
 
         let verity = verity::generate_initial_hashtree(&self.target, &hashfile)?;
 
-
         fs::write(outfile, verity.output())
             .context("failed to write veritysetup command output to a file")?;
 
@@ -122,7 +124,9 @@ impl UpdateBuilder {
 
     fn compress_image(&self) -> Result<()> {
         info!("Compressing image data");
-        util::xz_compress(&self.target)
+        util::exec_cmdline("xz", format!("-T0 {}", self.target.display()))
+            .context(format!("failed to decompress {}", self.target.display()))?;
+        Ok(())
     }
 
     fn write_final_image(&self) -> Result<()> {