Access control values
In some examples, a system receives, from a sender, an access control value generated based on information of a plurality of recipients. The system sends, to the sender, a signed version of the access control value for sending by the sender to the plurality of recipients with an encrypted message. The system receives, from a first recipient a request for a key to decrypt the encrypted message, a signed access control value and recipient information for deriving the access control value. The system determines whether the first recipient is one of the plurality of recipients using the signed access control value and the recipient information.
1. A non-transitory machine-readable storage medium storing instructions that upon execution cause a system to:
receive, from a sender, an access control value generated based on information of a plurality of recipients;
send, to the sender, a signed version of the access control value for sending by the sender to the plurality of recipients with an encrypted message;
receive, from a first recipient in association with a request for a key to decrypt the encrypted message, a signed access control value and recipient information for deriving the access control value, wherein the recipient information comprises an identity of the first recipient, and an intermediate value computed from information of another of the plurality of recipients; and
determine whether the first recipient is one of the plurality of recipients using the signed access control value and the recipient information.
2. The non-transitory machine-readable storage medium of claim 1 , wherein the instructions upon execution cause the system to:
send, to the sender, an identifier of the encrypted message;
receive, from the first recipient in association with the request for the key to decrypt the encrypted message, the identifier of the encrypted message; and
determine, based on the received identifier of the encrypted message, whether the first recipient is allowed to access the encrypted message.
3. The non-transitory machine-readable storage medium of claim 1 , wherein the intermediate value is based on application of a hash function on information of multiple recipients of the plurality of recipients.
4. The non-transitory machine-readable storage medium of claim 1 , wherein the access control value is based on a hash function applied on values derived from identities of the plurality of recipients.
5. The non-transitory machine-readable storage medium of claim 1 , wherein the access control value is based on hash values computed by applying a hash function on identities of recipients of the plurality of recipients.
6. The non-transitory machine-readable storage medium of claim 5 , wherein use of the hash values allows for the recipient information to include a compressed recipient list.
7. The non-transitory machine-readable storage medium of claim 1 , wherein the instructions upon execution cause the system to:
compute an access control value based on the recipient information;
compute a signed version of the computed access control value; and
compare the computed signed version of the computed access control value to the received signed access control value, to determine whether the first recipient is one of the plurality of recipients.
8. The non-transitory machine-readable storage medium of claim 7 , wherein the instructions upon execution cause the system to:
in response to determining that the first recipient is one of the plurality of recipients, send the key to the first recipient for use by the first recipient in decrypting the encrypted message.
9. The non-transitory machine-readable storage medium of claim 7 , wherein the instructions upon execution cause the system to:
send the key to the sender for use by the sender in encrypting a message to produce the encrypted message sent by the sender to the plurality of recipients.
10. The non-transitory machine-readable storage medium of claim 1 , wherein the instructions upon execution cause the system to:
receive, from the sender, a request to revoke access to the encrypted message, the request to revoke comprising a signed access control value and information useable to compute the access control value;
determine that the sender is authorized to revoke access to the encrypted message based on the signed access control value and the information in the request to revoke; and
revoke access to the encrypted message in response to the determining that the sender is authorized to revoke access to the encrypted message.
11. The non-transitory machine-readable storage medium of claim 10 , wherein the revoking of the access to the encrypted message comprises revoking access to the encrypted message by all recipients or by a set of recipients.
12. The non-transitory machine-readable storage medium of claim 10 , wherein the revoking of the access to the encrypted message comprises revoking access to the encrypted message based on time.
13. A sender device comprising:
a processor; and
a non-transitory storage medium storing instructions executable on the processor to:
compute an access control value based on:
applying a hash function on plural subsets of identities of a plurality of recipients, to produce respective intermediate hash values, and
applying the hash function on the intermediate hash values for producing the access control value;
send, to a key server, the access control value to request a key;
receive, from the key server, the key and a signed version of the access control value produced based on a signing function applied on the access control value from the sender device; and
send, to the plurality of recipients, a message encrypted with the key, and the signed version of the access control value.
14. The sender device of claim 13 , wherein the instructions are executable on the processor to:
received, from the key server, an identifier of the message, wherein the signed version of the access control value is produced based on the signing function applied on the identifier of the message and the access control value; and
send, to the plurality of recipients, the identifier of the message.
15. The sender device of claim 13 , wherein the instructions are executable on the processor to:
send, to the key server, a request to revoke access to the message by at least some of the plurality of recipients, the request to revoke comprising a signed access control value and information for use to compute the access control value.
16. A recipient device comprising:
a processor; and
a non-transitory storage medium storing instructions executable on the processor to:
receive, from a sender, an encrypted message and a signed access control value that are for receipt by a plurality of recipient devices from the sender;
to request a key from a key server, send, to the key server, the signed access control value and recipient information for use to derive an access control value, wherein the recipient information includes an identity of the recipient device and a hash value derived from identities of multiple other recipient devices, the signed access control value and the recipient information for use by the key server in verification that the recipient device is one of the plurality of recipient devices;
receive the key from the key server responsive to the verification; and
decrypt the encrypted message using the key.