Method to certify a trusted path (N1-N2-N3-N4) for transferring a given sensitive data flow in a software defined network comprising a plurality of nodes (N1, N2, N3, N4, N5), a trusted path enforcer, and a trusted path certifier; characterized in that it comprises the following steps: - sending at least one enforced flow rule, for configuring said trusted path, from the trusted path enforcer to flow rule certifiers (FRC1, FRC2, FRC3, FRC4) respectively embedded in or connected to all the nodes of the trusted path (N1, N2, N3, N4); - sending from each said flow rule certifier (FRC1, FRC2, FRC3, FRC4) to the trusted path certifier: -- a flow rule certificate (FRCA), if said flow rule certifier detects that an enforced flow rule it has received is actually satisfied by the configuration of the node where it is embedded in or connected to; -- a sensitive flow traces certificate (SFTC), if said flow rule certifier detects that the given sensitive data flow is actually crossing the node where it is embedded in or connected to; - collecting all the flow rule certificates (FRCA) sent, by the flow rule certifiers (FRC1, FRC2, FRC3, FRC4) respectively embedded in or connected to all the nodes of the trusted path (N1, N2, N3, N4), to the trusted path certifier, and deducing from them whether each enforced flow rule is satisfied, or not; - and collecting all the sensitive flow trace certificate (SFTC) sent, by the flow rule certifiers (FRC1, FRC2, FRC3, FRC4) respectively embedded in or connected to all the nodes of the trusted path (N1, N2, N3, N4), to the trusted path certifier and deducing from them whether the sensitive data flow has been correctly routed along the whole trusted path, or not. - sending at least one enforced flow rule, for configuring said trusted path, from the trusted path enforcer to flow rule certifiers (FRC1, FRC2, FRC3, FRC4) respectively embedded in or connected to all the nodes of the trusted path (N1, N2, N3, N4); - sending from each said flow rule certifier (FRC1, FRC2, FRC3, FRC4) to the trusted path certifier: -- a flow rule certificate (FRCA), if said flow rule certifier detects that an enforced flow rule it has received is actually satisfied by the configuration of the node where it is embedded in or connected to; -- a sensitive flow traces certificate (SFTC), if said flow rule certifier detects that the given sensitive data flow is actually crossing the node where it is embedded in or connected to; -- a flow rule certificate (FRCA), if said flow rule certifier detects that an enforced flow rule it has received is actually satisfied by the configuration of the node where it is embedded in or connected to; -- a sensitive flow traces certificate (SFTC), if said flow rule certifier detects that the given sensitive data flow is actually crossing the node where it is embedded in or connected to; - collecting all the flow rule certificates (FRCA) sent, by the flow rule certifiers (FRC1, FRC2, FRC3, FRC4) respectively embedded in or connected to all the nodes of the trusted path (N1, N2, N3, N4), to the trusted path certifier, and deducing from them whether each enforced flow rule is satisfied, or not; - and collecting all the sensitive flow trace certificate (SFTC) sent, by the flow rule certifiers (FRC1, FRC2, FRC3, FRC4) respectively embedded in or connected to all the nodes of the trusted path (N1, N2, N3, N4), to the trusted path certifier and deducing from them whether the sensitive data flow has been correctly routed along the whole trusted path, or not.