# Protection of Digital Elevation Model--One Approach
## 2 Materials and Methods
### Digital Signature Technology  
A digital signature is created by calculating the hash value of the message using a hash function. The resulting digital print is encrypted by the private key of the message signer using an asymmetric cryptographic algorithm. A digital signature is added to a message that is verified on the recipient's side to determine its authenticity.  
The digital signature confirms the authenticity and integrity of messages [41]. This means that if all conditions for a digital signature are met, the user who received the signed message can believe, with certainty, that the sender has created it (authenticity) and that the message has not been changed during the transfer. A digital signature ensures non-repudiation of the parties to the transaction, which means that the sender cannot successfully argue that the message is not signed until it disturbed the confidentiality of his private key. The requirement for non-repudiation should define how the participants in the transaction cannot subsequently deny their participation in all or only in some parts of the transaction.  
A digital signature represents an executed cryptographic action applied to the output of the hash function. A hash function is a function performing compression of input content into significantly smaller size output content known as digests, hash values, hashes, or hash codes.  
A cryptographic hash function has special characteristics suitable for cryptographic use. One of these functions used for digital signing belongs to the family of one-way functions. This family of functions within functions has the characteristics of simple calculations of any input, while the calculated output, which is random, cannot be converted into input [42]. It is characteristic that a minimal change in the input leads to a significant change in the output. By applying a one-way hash function to a document, it becomes computationally infeasible to find another document that hashes to the same value.  
Digital signing is a procedure for assigning a digital signature to a message (Figure 1). By using a one-way function, the message is transformed into a hash value, MD. Then, the hash value is encrypted by an asymmetric cryptographic algorithm (e.g., RSA) and the private key of the signer, PrKs. The value obtained is the digital signature of the message (MD) appended to the message, M.  
Verification of the digital signature is performed on the recipient side to establish that the signature is valid. Verification is performed by separating the digital signature from the message. The digital signature (DS) is converted by the same cryptographic algorithm (RSA) and the public key of the signer (PuKs) into a value hash. If the received hash value is equal to the hash value of the message, then the digital signature is valid. This means that the message has not been changed, that the signatory signed the message, and cannot claim that he has not signed the message. If the verification was not successful, then the integrity of the message, authenticity of the signer, and non-repudiation are jeopardized.