Subscriber identity privacy

A method performed by a cellular communication device with a first subscriber information module (SIM) that specifies a first home network and an unconcealed first subscriber identifier, the method comprising:

• determining that (a) a concealed first subscriber identifier is unavailable from the first SIM and (b) no encryption key for encrypting the unconcealed first subscriber identifier is available from the first SIM;
• determining that a home network key of the first home network is not stored in a memory of the cellular communication device;
• in response to determining that the home network key of the first home network is not stored in the memory of the cellular communication device, sending the unconcealed first subscriber identifier for authentication by the first home network;
• determining that (c) a concealed second subscriber identifier is unavailable from a second SIM that specifies a second home network and an unconcealed second subscriber identifier and (d) no encryption key for encrypting the unconcealed second subscriber identifier is available from the second SIM;
• determining that a home network key of the second home network is stored in the memory of the cellular communication device;
• obtaining the unconcealed second subscriber identifier from the second SIM;
• encrypting the unconcealed second subscriber identifier using the home network key of the second home network to create the concealed second subscriber identifier;
• and
• sending the concealed second subscriber identifier for authentication by the second home network.

A cellular communication device comprising:

• one or more processors;
• and
• one or more non-transitory computer-readable media storing computer-executable instructions that, when executed by the one or more processors, cause the one or more processors to perform actions comprising:
• determining that (a) a concealed first subscriber identifier is unavailable from a first subscriber information module (SIM) and (b) no encryption key for encrypting an unconcealed first subscriber identifier is available from the first SIM;
• determining that (c) the first SIM specifies a first home network and (d) a home network key of the first home network is stored by the one or more non-transitory computer-readable media;
• obtaining the unconcealed first subscriber identifier from the first SIM;
• obtaining the home network key of the first home network from the one or more non-transitory computer-readable media;
• encrypting the unconcealed first subscriber identifier using the home network key of the first home network to create the concealed first subscriber identifier;
• sending the concealed first subscriber identifier for authentication by the first home network;
• determining that (e) a concealed second subscriber identifier is unavailable from a second SIM that specifies a second home network and an unconcealed second subscriber identifier and (f) no encryption key for encrypting the unconcealed second subscriber identifier is available from the second SIM;
• determining that a home network key of the second home network is stored by the one or more non-transitory computer-readable media;
• obtaining the unconcealed second subscriber identifier from the second SIM;
• encrypting the unconcealed second subscriber identifier using the home network key of the second home network to create the concealed second subscriber identifier;
• and
• sending the concealed second subscriber identifier for authentication by the second home network.