Trying to get a clue about 3DES

Michael Roth mroth at
Thu Jan 7 15:33:58 CET 1999

On 6 Jan 1999, Stainless Steel Rat wrote:

> When encrypting a message, GPG randomly generates three 56-bit DES session
> keys (key1, key2, key3). The message is encrypted with key1, decrypted

Not exactly. GPG randomly generates three 64-bit DES keys.
According to the DES specification, a 64-bit DES key normally includes
eight parity bits which are not used for encryption or decryption,
resulting in 56 bits used for encryption/decryption.
In GPG and most software today, the parity bits are just ignored. They
only protect the key from changing during transport (The DES designers
thought keys will be written down to paper and will be entered in some
crypto machines by keyboard and so on).
The parity bits don't affect the DES algorithm in any way. They will be
not used by the DES algorithm.


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