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Data Management
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Encrypted Storage and Hydra

What is Hydra?

Hydra is encrypted file storage solution. It encrypts files and stores them on normal storage elements (storage elements are not part of the Hydra service - any SE supported by GFAL library can be used for that). The sensitive information is the encryption key, which is after generation splitted and distributed on several different places, called the Hydra Keystores (Hydra Servers or services).

The reason for the splitting is that the encryption key can't be reconstructed from the one piece only, i.e. if one of the Hydra server gets compromised, the hacker cannot decrypt the files. Splitting algorithm (SSSS) is however also fault tolerant: the encryption key can be reconstructed if at least some (predefined) count of the pieces can be found (this is normally more than one but less than all). Thus even if one Hydra service does not work, the key can be reconstructed from the rest of the pieces.


Hydra is released in Glite 3.1 Update 38.

Hydra Server

The Hydra server consists of a MySQL database and a Tomcat server which runs the actual hydra software (java). The hyrda server stores only key pieces and related ACL information into MySQL database, not any files.

installation of the service

One has to install at least one Hydra service (glite-data-hydra-service) and must have some storage element. There is separate glite-yaim-hydra package to help configure the Hydra service(s) by YAIM tool. Note! The next message is displayed when running yaim for the first time:

  ERROR 1045 (28000): Access denied for user 'hydra1'@'localhost' (using password: YES)
Message above is a cosmetic warning and can be skipped (bug #43945).

Each server must have MySQL database and Tomcat-server with valid host certificates. Please have a look at JPackage installation for the basic Java packages.

For test purposes one server can run several hydra services (e.g. 1 MySQL, 3 MySQL databases, 1 Tomcat, 3 webapps).

test configuration of the service

For test purposes one can configure all Hydra service instances on the same node - in production environment this doesn't make sence. You can use this configuration example, where the administrator's DN could be the host itself, what you can get as

  openssl x509 -in /etc/grid-security/hostcert.pem -subject -noout

Configuration file:


You can use this configuration directly with the /opt/glite/etc/glite-data-hydra-service/configure command or by appending it to the YAIM configuration node and executing

  /opt/glite/yaim/bin/yaim -c -s /opt/glite/yaim/etc/site-info.def -n HYDRA

If you have installed glite-data-hydra-cli you can test the configuration by

  source /opt/glite/etc/profile.d/
  glite-eds-key-register testkey
  glite-eds-key-unregister testkey

The log files of the hydra services are located at /var/log/tomcat5/glite-data-hydra-service-<instance>.log

You can also test the BDII info provider locally:

  source /opt/glite/etc/profile.d/
  export GLITE_SD_PLUGIN=bdii
  export LCG_GFAL_INFOSYS=localhost:2170
  glite-sd-query -t org.glite.Metadata
  glite-eds-key-register testkey
  glite-eds-key-unregister testkey

distributed configuration of the service

In a real installation you would have to install the Hydra services on different hosts. If they are on,,, then the confiuguration files would be:







Hydra Client

Hydra client is collection of glite-eds-* commands and a hydra-cli library to en/decrypt files and to control hydra keys.

installation of the client

On the UI and WN one needs the client package (glite-data-hydra-cli) with all of its dependencies.

configuration of the client

The client requires some information of the current Hydra servers, this can be a local file (for test purposes) or any information system (e.g. BDII).

/opt/glite/share/doc/glite-data-hydra-cli/ is a good starting point for test configuration. In this case you should define SD environment variables pointing to your local file

  export GLITE_SD_PLUGIN=file
  export GLITE_SD_SERVICES_XML=/path/to/hydra-services.xml

You must also have valid X509 user certificate (environment variables X509_USER_CERT and X509_USER_KEY).

client usage

One could store a file on the local storage element of the UI:

  glite-eds-put -i $ID picture rfio:////dpm/$ID

Note! There is a bug (#41592) in the glite-eds-put: you must specify the ID with -i option, because the command can't generate the GUID for the file correctly in all cases.

The file could be accessed for local processing:

  glite-eds-get -i $ID rfio:////dpm/$ID picture
  display picture

This copies the file content dencrypted to the local disk, which might not be desirable. One can avoid this step, by directly using the hydra-cli libraries from the application directly. In this case the content is only decrypted in the memory.

Later the user may delete the sensitive file along with its keys:

  rfio-rm rfio:////dpm/$ID
  glite-eds-rm $ID

Usecase: DPM SE with DICOM backend

For DICOM the special DPM server should be installed as back-end.

Solution : Extension of the DPM storage element to support DICOM as storage back-end.

  • File encryption on the fly, local decryption
  • Use of HYDRA for split key management
  • Use of the LFC to register/retrieve system data
  • Replicas location, filesize, ...
  • Use of srmv2 to get the turls
  • Use of block I/O protocols, gridftp to load medical images
  • Access control based on VOMS


Using the distributed Hydra keystore

  • the file ID=/study/series/SOP ID
  • uses DPM with DICOM back-end
  • LFN=lfn-prefix/study/series/SOP ID
  • SURL=se-prefix/study/series/SOP ID

The back-end is part of a standard DPM service:


  dpm-dicom-trigger MDM_test-0.78/test/dicom/jm0301-00032.dcm

What happens in details:

  • uploads a file to DICOM
  • fetches the file from DICOM (file size may change!)
  • calculates the encrypted size and ID, for example:
  • ID=/1.2.826.0.1.3680043.2.1143..20060202124502298.29/1.2.826.0.1.3680043.2.1143..20060202124502298.29/1.2.826.0.1.3680043.2.1143..20060202124504468.51
  • calls 'dpm-register' to register the file into DPM with the SFN /dpm/<domain>/home/biomed/mdm/<ID> and with the PFN dicom:///<ID> and marked as near-line copy
  • calls 'glite-eds-register' to create an en/decryption key and adds the DPM host to be able to read it (i.e. glite-eds-setacl)
  • optionally: registers the file in LFC with the LDN /grid/biomed/mdm/<ID>
  • optionally: registers the file metadata in AMGA


The encrypted file can be replicated and retrieved from any other SE.

DPM I/O access via: gridftp, rfio(s), http(s)


Example with separate download an decryption steps:

  lcg-cp -bD srmv2 srm://<ID> file:picture.enc 
  glite-eds-decrypt <ID> picture.enc picture

One can do the same with one command:

  glite-eds-get -i <ID> rfio:////dpm/<ID> picture

the details in this case:

  • file is opened via gfal_open()
  • decryption key is fetched for <ID>
  • loop on gfal_read(), glite_eds_decrypt_block(), write()

'glite-eds-get' is a simple utility over the EDS library.


DICOM files are marked as 'nearline', which have to be recalled to disk nearline TURL is "study/series/SOP ID" a DPM-DICOM recall daemon processes multi-file recalls from DICOM to disk during the recall the DICOM files are anonymized and encrypted DPM serves the encrypted files normally.


DPM-DICOM recall daemon with multiple multi-file requests: DPM starts the retrieval by a direct call, however jobs are also stored in DB recall daemon manages the DB and DPM interactions and calls a plug-in for each PFN (see dicom:///<ID>) simple plug-in interface, within a shared library in

  int dpm_dicomcopyfile (char *dicom_fn, char *turl, int *errcode, char *errbuf)
The plug-in then retrieves the encryption key from Hydra, retrieves the file from DICOM and stores the file via rfio.

Technical background

Old working page of DMEncryptedStorage!

What is SSSS?

Shamir's Secret Sharing Scheme is a library to split keys for reliability and security reasons. The Hydra client library uses SSSS to split and merge encryption keys.

However there is also a simple binary to make use of the library alone:

  $ glite-ssss-split-passwd -q 5 3 secret
  137c9547aba101ef 6ee7adbbaacac1ef 1256bcc160eda592 fdabc259cdfbacc9 3113be83f203d794
  $ glite-ssss-join-passwd -q 137c9547aba101ef NULL 1256bcc160eda592 NULL 3113be83f203d794

In the hydra client the minimum count (N) of the needed pieces to reconstruct the key is calculated from the total count (M) of the pieces (i.e. number of the servers): N = ceil(log2( M + 1 )). I.e. for 2-3 servers 2 pieces is required, for 4-7 servers 3 pieces is required, etc.

Explanation of key register


Current Hydra service install commands.




  • EGEE-JRA1 All Hands Meeting, 2006-07 pdf odp

  • CHEP Poster, 2007-09 pdf odg

  • EGEE JRA1 All Hands Meeting, 2007-10 pdf odp

  • Internal MDM Demo, 2007-12 * pdf * odp

Last edit: JohnWhite on 2012-10-26 - 14:19

Number of topics: 1

Maintainer: JoniHahkala, AkosFrohner

Topic attachments
I Attachment History Action Size Date Who Comment
Unknown file formatodp EGEE-JRA1-All-Hands-2007-10-25-MDM.odp r1 manage 776.6 K 2008-09-01 - 11:36 AkosFrohner  
PDFpdf EGEE-JRA1-All-Hands-2007-10-25-MDM.pdf r1 manage 302.0 K 2008-09-01 - 11:30 AkosFrohner EGEE JRA1 All Hands Meeting, 2007-10
Unknown file formatodp EGEE-JRA1-All-Hands-EDS-MDM-20060711.odp r1 manage 231.4 K 2008-09-01 - 11:38 AkosFrohner  
PDFpdf EGEE-JRA1-All-Hands-EDS-MDM-20060711.pdf r1 manage 131.9 K 2008-09-01 - 11:27 AkosFrohner EGEE-JRA1 All Hands Meeting, 2006-07
PNGpng Hydra-standalone.png r1 manage 35.0 K 2008-04-04 - 11:59 AkosFrohner  
PDFpdf Hydra_User_Guide.pdf r1 manage 442.1 K 2012-10-26 - 14:19 JohnWhite  
PNGpng MDM-DPM-DICOM-retrieval.png r1 manage 33.4 K 2008-04-04 - 11:59 AkosFrohner  
PNGpng MDM-DPM-DICOM-trigger.png r1 manage 35.2 K 2008-04-04 - 12:00 AkosFrohner  
Unknown file formatodp MDM-demo.odp r1 manage 785.5 K 2008-09-01 - 11:36 AkosFrohner  
PDFpdf MDM-demo.pdf r1 manage 840.6 K 2008-09-01 - 11:35 AkosFrohner Internal MDM Demo, 2007-12
PNGpng MDM-retrieval.png r1 manage 43.3 K 2008-04-04 - 12:00 AkosFrohner  
Unknown file formatodg chep07_poster_MDM.odg r1 manage 1336.5 K 2008-09-01 - 11:37 AkosFrohner  
PDFpdf chep07_poster_MDM.pdf r1 manage 521.3 K 2008-09-01 - 11:29 AkosFrohner CHEP Poster, 2007-09
PNGpng eds-overview.png r1 manage 21.7 K 2006-03-06 - 13:49 UnknownUser  
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