m4_comment([$Id: encrypt.so,v 11.13 2007/03/27 14:20:56 sue Exp $])

m4_ref_title(Environment, Encryption, @encryption, env/security, env/remote)

m4_p([dnl
m4_db optionally supports encryption using the Rijndael/AES (also known
as the Advanced Encryption Standard and Federal Information Processing
Standard (FIPS) 197) algorithm for encryption or decryption.  The
algorithm is configured to use a 128-bit key.  m4_db uses a 16-byte
initialization vector generated using the Mersenne Twister.  All
encrypted information is additionally checksummed using the SHA1 Secure
Hash Algorithm, using a 160-bit message digest.])

m4_p([dnl
The encryption support provided with m4_db is intended to protect
applications from an attacker obtaining physical access to the media on
which a m4_db database is stored, or an attacker compromising a system
on which m4_db is running but who is unable to read system or process
memory on that system.
m4_bold([dnl
The encryption support provided with m4_db will not protect applications
from attackers able to read system memory on the system where m4_db is
running.])])

m4_p([dnl
Encryption is not the default for created databases, even in database
environments configured for encryption.  In addition to configuring for
encryption by calling the m4_ref(dbenv_set_encrypt) or
m4_refT(dbh_set_encrypt)s, applications must specify the
m4_ref(DB_ENCRYPT) flag before creating the database in order for the
database to be encrypted.  Further, databases cannot be converted to an
encrypted format after they have been created without dumping and
re-creating them.  Finally, encrypted databases cannot be read
on systems with a different endianness than the system that created
the encrypted database.])

m4_p([dnl
Each encrypted database environment (including all its encrypted
databases) is encrypted using a single password and a single algorithm.
Applications wanting to provide a finer granularity of database access
must either use multiple database environments or implement additional
access controls outside of m4_db.])

m4_p([dnl
The only encrypted parts of a database environment are its databases
and its log files. Specifically, the m4_link(M4RELDIR/ref/env/region,
[shared memory regions]) supporting the database environment are not
encrypted.  For this reason, it may be possible for an attacker to read
some or all of an encrypted database by reading the on-disk files that
back these shared memory regions.  To prevent such attacks, applications
may want to use in-memory filesystem support (on systems that support
it), or the m4_ref(DB_PRIVATE) or m4_ref(DB_SYSTEM_MEM) flags to the
m4_refT(dbenv_open), to place the shared memory regions in memory that
is never written to a disk.  As some systems page system memory to a
backing disk, it is important to consider the specific operating system
running on the machine as well.  Finally, when backing database
environment shared regions with the filesystem, m4_db can be configured
to overwrite the shared regions before removing them by specifying the
m4_ref(DB_OVERWRITE) flag.  This option is only effective in the
presence of fixed-block filesystems, journaling or logging filesystems
will require operating system support and probably modification of the
m4_db sources.])

m4_p([dnl
While all user data is encrypted, parts of the databases and log files
in an encrypted environment are maintained in an unencrypted state.
Specifically, log record headers are not encrypted, only the actual log
records.  Additionally, database internal page header fields are not
encrypted.  These page header fields includes information such as the
page's m4_ref(DbLsn), number, and position in the database's sort
order.])

m4_p([dnl
Log records distributed by a replication master to replicated clients are
transmitted to the clients in unencrypted form.  If encryption is
desired in a replicated application, the use of a secure transport
is strongly suggested.])

m4_p([dnl
We gratefully acknowledge:])

m4_bulletbegin
m4_bullet([dnl
Vincent Rijmen, Antoon Bosselaers and Paulo Barreto for writing the
Rijndael/AES code used in m4_db.])
m4_bullet([dnl
Steve Reid and James H. Brown for writing the SHA1 checksum code used
in m4_db.])
m4_bullet([dnl
Makoto Matsumoto and Takuji Nishimura for writing the Mersenne Twister
code used in m4_db.])
m4_bullet([dnl
Adam Stubblefield for integrating the Rijndael/AES, SHA1 checksum and
Mersenne Twister code into m4_db.])
m4_bulletend

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