IEEE 1609.2b-2019 pdf download

IEEE 1609.2b-2019 pdf download.IEEE Standard for Wireless Access in Vehicular Environments—Security Services for Applications and Management Messages Amendment 2: PDU Functional Types and Encryption Key Management
5.3.4.1 General
The SDS generates encrypted data on request from the SDEE. In the request, the SDEE may provide the SDS with a list of recipient keys. The SDEE may also request the SDS to include a direct indication of the data encryption key.
This enables the SDEE to encrypt data for multiple recipients, each of which it believes can decrypt that data. The encryption process proceeds as follows: First, the data is encrypted with a symmetric data encryption key k to produce a SymmetricCiphertext as specified in 5.3.4.2. The data encryption key k can be obtained by the SDS in a number of ways, including the following:
A pre-stored key
A key that was made available by the SDEE to the recipient through an earlier SPDU containing an encrypted data encryption key, and stored at the SDS
A key that was made available to the SDEE by the recipient through an earlier SPDU containing an encrypted data encryption key, and stored at the SDS
A key that was made available to the SDEE by another SDEE through an earlier SPDU containing an encrypted data encryption key, and stored at the SDS
A key which has been generated for an earlier SPDU to another recipient
An “ephemeral” key which is generated appositely for that SPDU and only used once
If the key was not “ephemeral”, i.e., generated within the SDS at the time of data encryption, it is referred to as “static”. Following data encryption, the SDS creates RecipientInfos which allow the intended recipients to access the data encryption key. Each different key encryption key i will in general correspond to a different intended recipient of the encrypted PDU. The recipients are provided information about the data encryption key as follows:
If the invoking SDEE provided one or more recipient keys, the SDS encrypts the key k with each of those key keys to produce a series of encrypted keys {ek i }, with each ek i an encryption of k with key encryption key i. This process is specified in 5.3.4.3. For each key encryption key i, the SDS creates a RecipientInfo structure containing the encrypted key ek i , of the type determined by the type of the recipient’s encryption key as specified in 6.3.37. This enables the recipients in possession of the corresponding decryption key to recover the data encryption key.
If the invoking SDEE requested a direct indication of the data encryption key, the SDS creates a single RecipientInfo structure of type PreSharedKeyRecipientInfo identifying the data encryption key. This enables recipients who already possess the data encryption key to identify that it is the key to be used to decrypt the encrypted data.
The SDS then encodes all the RecipientInfos into a SequenceOfRecipientInfo, encodes the SequenceOfRecipientInfo and the SymmetricCiphertext into an EncryptedData, and encapsulates the EncryptedData in an Ieee1609Dot2Data. This approach allows an EncryptedData to be created for recipients that already know the data encryption key, for recipients that do not already know the data encryption key, or for a combination of the two types of recipients.
In the Sec-EncryptedData.request primitive of 9.3.11.1, the SDEE indicates to the SDS whether to use an ephemeral or static data encryption key by providing or not providing the Data Encryption Key Type parameter. If the SDEE requested an ephemeral data encryption key, the SDS may return a cryptomaterial handle (see 4.3.3 and 9.2.2) for that data encryption key in the corresponding Sec-EncryptedData.confirm primitive to enable that data encryption key to be reused if desired. In the Sec-EncryptedDataDecryption.confirm primitive of 9.3.13.2, the SDS may provide a Cryptomaterial Handle for the data encryption key in the Data Encryption Key CMH parameter. This enables the SDEE that receives this primitive to store the CMH for later use.
5.3.4.2 Data encryption Data encryption is performed as follows:
The plaintext P has the form of a valid encoded Ieee1609Dot2Data structure.
A symmetric data encryption key k for an approved symmetric algorithm as specified in 5.3.8 is available as described in 5.3.4.1.
P is encrypted with k to obtain a ciphertext C. If the approved symmetric algorithm uses a nonce, that nonce is generated freshly and at random for each new plaintext.
The ciphertext C is encoded as a SymmetricCiphertext.IEEE 1609.2b pdf download.IEEE 1609.2b-2019 pdf download