Russ,
Since we are working on an update to RFC 3280, I propose the following
revisions to these descritions.
The keyEncipherment bit is asserted when the subject public key is
used for key transport. For example, when an RSA key is to be
used for key management by encrypting a symmetric content-encryption
key, then this bit shall asserted.
The dataEncipherment bit is asserted when the subject public key
is used for directly enciphering raw user data without the use of
an intermediate symmetric cipher.
Thank you for this strawman proposal. I would rather propose:
The keyEncipherment bit is asserted when the subject public key is
used for enciphering private or secret keys, i.e. for key transport.
For example, this bit shall be set when a public RSA key is to be
used for encrypting a symmetric content-decryption key or an
asymmetric private key.
The dataEncipherment bit is asserted when the subject public key
is used for directly enciphering raw user data without the use of
an intermediate key.
Reasons:
a) "Key transport" is not explicit enough. The purpose is to encipher
either a private key or a secret key.
b) The example is not clear enough: "RSA key" can be a private key or a
public key, hence why "public" has been added.
c) The key that is communicated is a decryption key rather than an
encryption key, hence why "content-encryption" has been changed into
"content-decryption".
d) The example has been extended to cover the case of an asymmetric cipher
as well.
e) In the last statement, the intermediate key would not necessarily be a
symmetric cipher, hence why "symmetric" has been deleted. Also "cipher"
has been replaced by "key'.
Note that the current text from X.509 is:
c) keyEncipherment: for enciphering keys or other security information,
e.g. for key transport;
d) dataEncipherment: for enciphering user data, but not keys or other
security information as in c) above;
Denis