Whatever place TextSecure is getting the key from could have replaced your girlfriend key with something else and be MITMing all the traffic.
The proper way to do this would be to have your girlfriend's phone display a QR code with her public key and have you scan it with your phone camera, or using NFC to transfer the public key if available.
Whatever place TextSecure is getting the key from could have replaced your girlfriend key with something else and be MITMing all the traffic.
The proper way to do this would be to have your girlfriend's phone display a QR code with her public key and have you scan it with your phone camera, or using NFC to transfer the public key if available.