Configure the private keys for the signature in the file blobstore-rest.xml :
<filters> <filter> <filter-name>CRMRestSecurity</filter-name> <url-pattern>/rest/blobstore/*</url-pattern> <filter-class>fr.paris.lutece.util.signrequest.servlet.HeaderHashRequestFilter</filter-class> <init-param> <param-name>elementsSignature</param-name> <param-value>blob_key</param-value> </init-param> <init-param> <param-name>validityTimePeriod</param-name> <param-value>0</param-value> </init-param> <init-param> <param-name>privateKey</param-name> <param-value>change me</param-value> </init-param> </filter> </filters>