A real-time electronic signature validation (RTESV) system, said system comprising: at least one stationary central computer system including a ground mobile user account management (GMUAM) module, the GMUAM module comprising a GMUAM user database that is updatable by an enterprise user system to have stored thereon up-to-date authorized user account information; and at least one onboard computer system hosted by at least one mobile system, each OCS including: a mobile user account management (MUAM) module adapted to communicate with the GMUAM module, the MUAM module comprising a MUAM user database that is updated by the GMUAM module to have stored thereon the up-to-date authorized user account information stored on the GMUAM user database, characterized by each OCS further including: a subsystem of the OCS that receives an entry made by a user using the OCS and is adapted to compute a cryptographic hash, to sign the hash, and to retrieve a dynamic certificate created by an intermediate certificate authority that includes a first identifier which is uniquely associated with the OCS from which the entry was created, and a second identifier which identifies a mobile vehicle that the OCS is located on; and a signature validator module communicatively connected to the MUAM module to access the MUAM user database and verify whether user account information included in an electronic signature initiated by a secure data application hosted by the OCS is authorized user account information, wherein the at least one mobile system is located on the mobile vehicle. at least one stationary central computer system including a ground mobile user account management (GMUAM) module, the GMUAM module comprising a GMUAM user database that is updatable by an enterprise user system to have stored thereon up-to-date authorized user account information; and at least one onboard computer system hosted by at least one mobile system, each OCS including: a mobile user account management (MUAM) module adapted to communicate with the GMUAM module, the MUAM module comprising a MUAM user database that is updated by the GMUAM module to have stored thereon the up-to-date authorized user account information stored on the GMUAM user database, characterized by each OCS further including: a subsystem of the OCS that receives an entry made by a user using the OCS and is adapted to compute a cryptographic hash, to sign the hash, and to retrieve a dynamic certificate created by an intermediate certificate authority that includes a first identifier which is uniquely associated with the OCS from which the entry was created, and a second identifier which identifies a mobile vehicle that the OCS is located on; and a signature validator module communicatively connected to the MUAM module to access the MUAM user database and verify whether user account information included in an electronic signature initiated by a secure data application hosted by the OCS is authorized user account information, wherein the at least one mobile system is located on the mobile vehicle. a subsystem of the OCS that receives an entry made by a user using the OCS and is adapted to compute a cryptographic hash, to sign the hash, and to retrieve a dynamic certificate created by an intermediate certificate authority that includes a first identifier which is uniquely associated with the OCS from which the entry was created, and a second identifier which identifies a mobile vehicle that the OCS is located on; and a first identifier which is uniquely associated with the OCS from which the entry was created, and a second identifier which identifies a mobile vehicle that the OCS is located on; and a signature validator module communicatively connected to the MUAM module to access the MUAM user database and verify whether user account information included in an electronic signature initiated by a secure data application hosted by the OCS is authorized user account information,