Method for securing/unsecuring data exchanged by communication nodes, the method comprising: • generating, by a first communication node and by one or more second communication node(s), one and the same ordered sequence of security keys, each of which is to be used in a respective validity time interval; • synchronizing, by each of the first and second communication nodes (5,8), a respective internal time reference to a global time reference thereby obtaining a respective sync time reference; • extracting, by the first communication node, a security key from said one and the same ordered sequence of security keys on the basis of the respective sync time reference; • securing, by the first communication node, data to be sent to the second communication node(s) on the basis of the extracted security key; • extracting, by each second communication node, a respective ordered group of security keys from said one and the same ordered sequence of security keys on the basis of the respective sync time reference; and • unsecuring, by each second communication node, the secured data received from the first communication node on the basis of the respective ordered group of security keys extracted; the method being characterized in that each second communication node: • tries unsecuring the secured data received from the first communication node by - following a respective given sequence of unsecuring attempts, each of which is based on a corresponding security key included in the respective ordered group of security keys extracted, and - starting with an unsecuring attempt based on a security key that is in a respective starting position in the respective ordered group of security keys extracted; • modifies the respective starting position so as to compensate for a respective propagation delay estimated for previous secured data sent by the first communication node and received by said second communication node; and • determines, on the basis of said respective propagation delay, a respective number of security keys to be included in the respective ordered group of security keys to be extracted. • generating, by a first communication node and by one or more second communication node(s), one and the same ordered sequence of security keys, each of which is to be used in a respective validity time interval; • synchronizing, by each of the first and second communication nodes (5,8), a respective internal time reference to a global time reference thereby obtaining a respective sync time reference; • extracting, by the first communication node, a security key from said one and the same ordered sequence of security keys on the basis of the respective sync time reference; • securing, by the first communication node, data to be sent to the second communication node(s) on the basis of the extracted security key; • extracting, by each second communication node, a respective ordered group of security keys from said one and the same ordered sequence of security keys on the basis of the respective sync time reference; and • unsecuring, by each second communication node, the secured data received from the first communication node on the basis of the respective ordered group of security keys extracted; • tries unsecuring the secured data received from the first communication node by - following a respective given sequence of unsecuring attempts, each of which is based on a corresponding security key included in the respective ordered group of security keys extracted, and - starting with an unsecuring attempt based on a security key that is in a respective starting position in the respective ordered group of security keys extracted; - following a respective given sequence of unsecuring attempts, each of which is based on a corresponding security key included in the respective ordered group of security keys extracted, and - starting with an unsecuring attempt based on a security key that is in a respective starting position in the respective ordered group of security keys extracted; • modifies the respective starting position so as to compensate for a respective propagation delay estimated for previous secured data sent by the first communication node and received by said second communication node; and • determines, on the basis of said respective propagation delay, a respective number of security keys to be included in the respective ordered group of security keys to be extracted.