Configuration File Compression; File Encryption - Cisco SPA921 - - IP Phone Provisioning Manual

Creating Provisioning Scripts
Open Format Configuration File
NOTE
Cisco Small Business IP Telephony Devices Provisioning Guide

Configuration File Compression

Optionally, the XML configuration profile can be compressed to reduce the
network load on the provisioning server. The supported compression method is
the gzip deflate algorithm (RFC1951). The gzip utility and a compression library
that implements the same algorithm (zlib) are readily available from Internet sites.
To identify when compression is applied, the IP Telephony Device expects the
compressed file to contain a gzip compatible header, as generated by invoking the
gzip utility on the original XML file.
For example, if profile.xml is a valid profile, the file profile.xml.gz is also accepted.
This example can be generated with either of the following commands:
# first invocation, replaces original file with compressed file:
gzip profile.xml
# second invocation, leaves original file in place, produces new compressed
file:
cat profile.xml | gzip > profile.xml.gz
The IP Telephony Device inspects the downloaded file header to determine the
format of the file. The choice of file name is not significant and any convention that
is convenient for the service provider can be used.

File Encryption

An XML configuration profile can be encrypted using symmetric key encryption,
whether or not it is already compressed. The supported encryption algorithm is
the American Encryption Standard (AES), using 256-bit keys, applied in cipher
block chaining mode.
Compression must precede encryption for the IP Telephony Device to recognize a
compressed and encrypted XML profile. First generate the XML, then compress
with gzip, and finally encrypt.
The OpenSSL encryption tool, available for download from various Internet sites,
can be used to perform the encryption. Note that support for 256-bit AES
encryption may require recompilation of the tool (so as to enable the AES code).
The firmware has been tested against version openssl-0.9.7c.
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