Method for providing end-to-end security of a communication between at least one first item of terminal equipment and one second item of terminal equipment, communication being established using a session initiation protocol allowing exchange of session keys, each item of terminal equipment using a session key to encrypt the communication data which it transmits, the session keys being exchanged securely via an intermediate server using a security certificate (230.3), characterised in that the method carries out the following steps carried out by the intermediate server: - reception of a first invite message, the first item of terminal equipment inviting the second item of terminal equipment, the first invite message comprising at least one attribute describing a first session key; - production of a second invite message, the first item of terminal equipment inviting the second item of terminal equipment, the second invite message comprising: o a first session key, the first session key being configured by the intermediate server according to the attribute describing the first session key, the first session key being designed to be used to encrypt/decrypt the data transmitted by the first item of terminal equipment; o at least one second session key, the second session key being configured by the intermediate server, the second session key being designed to be used to encrypt/decrypt the data transmitted by the second item of terminal equipment; - transmission of the second invite message; - reception of a first accept message, the second item of terminal equipment accepting the invitation; - production of a second accept message, the second item of terminal equipment accepting the invitation, the second accept message comprising: o the first session key; o the at least one second session key; - transmission of the second accept message. - reception of a first invite message, the first item of terminal equipment inviting the second item of terminal equipment, the first invite message comprising at least one attribute describing a first session key; - production of a second invite message, the first item of terminal equipment inviting the second item of terminal equipment, the second invite message comprising: o a first session key, the first session key being configured by the intermediate server according to the attribute describing the first session key, the first session key being designed to be used to encrypt/decrypt the data transmitted by the first item of terminal equipment; o at least one second session key, the second session key being configured by the intermediate server, the second session key being designed to be used to encrypt/decrypt the data transmitted by the second item of terminal equipment; o a first session key, the first session key being configured by the intermediate server according to the attribute describing the first session key, the first session key being designed to be used to encrypt/decrypt the data transmitted by the first item of terminal equipment; o at least one second session key, the second session key being configured by the intermediate server, the second session key being designed to be used to encrypt/decrypt the data transmitted by the second item of terminal equipment; - transmission of the second invite message; - reception of a first accept message, the second item of terminal equipment accepting the invitation; - production of a second accept message, the second item of terminal equipment accepting the invitation, the second accept message comprising: o the first session key; o the at least one second session key; o the first session key; o the at least one second session key; - transmission of the second accept message.