NIH Human Microbiome Project 2

Aspera Key Authentication

The iHMP DCC Aspera server supports authentication via SSH keys to allow for quick and easy transfers without manually entering a password. The iHMPDCC is now accepting the public SSH keys for individuals who wish to make use of this authentication method.

Generating SSH Keys

Generating keys can easily be done on the Linux, Mac OSX or Windows platform using a variety of tools:

Linux and Mac OSX:

Generating a set of keys on the Linux or Mac OSX platform can be done using the built-in ssh-keygen utility. Executing the ssh-keygen command will start the process of generating a keypair:


A series of questions will need to be answered to successfully generate a pair of keys.

Enter file in which to save the key (/home/user/.ssh/id_rsa):

By default, the directory where the keys are saved is the user's ~/.ssh directory. Any directory can be used, however, please make a note of your chosen location since the private key generated will be needed when transferring data to or from the DCC Aspera server. Also provide the basename used to name the keys (in this case "dcc_aspera"):

Enter file in which to save the key (/home/user/.ssh/id_rsa): /home/user/dcc_aspera

Next, you will be prompted for a passphrase:

Enter passphrase (empty for no passphrase):

This should be left empty and can be done so by simply hitting the ENTER key twice to proceed.

Your identification has been saved in /home/user/dcc_aspera. Your public key has been saved in /home/user/
The key fingerprint is:

Two keys will be generated and deposited in the folder specified:

ls -ltrh /home/user
-rw------- 1 user group 1.7K Oct 19 15:33 dcc_aspera
-rw-r--r-- 1 user group 414 Oct 19 15:33


Generating a set of SSH keys can be done on the Windows operating system using the puttygen utility. It can be downloaded via the following URL:

With the PuTTYgen binary/executable open the process is as following:


Make sure the 'SSH-2 RSA' option is checked and the "Number of bits in a generated key" is set to 1024 and click the "Generate" button to begin the key generation.


Follow the onscreen instructions and move the mouse over the area found right under the progress bar to generate the randomness needed for the key. Once this is done your key should be displayed on screen.


Make sure to leave the "Key passphrase" box empty and click on the "Save private key" button. This should pop open a open a dialog box asking you if you are sure that you do want to save the key without a passphrase, which we do want to do so click ok and save both the public key and the private key.

Associating an account with SSH keys

The ".pub" file of these should be attached to an email sent to with a subject of "iHMP-DCC ASPERA ACCESS". The body of the email should state which user the keys should be associated with. Currently the iHMPDCC does not permit the issuance of keys for generic use by organizations. Keys are only associated with individual users.

Transferring files with Aspera and SSH Keys

Once a public key has been received and associated with an account, downloading is as easy as adding one more parameter to your ascp command:

ascp -i /path/to/private/key

Or when uploading a file:

ascp -i /path/to/private/key -l100M /path/to/file/to/upload \

Examples are shown below:

ascp -i /home/user/dcc_aspera

ascp -i /home/user/dcc_aspera -l100M /local/scratch/huge_genome.tar