## 5 Conclusions  
The purpose of cryptography is to protect data from unauthorized use. The cryptographic method offers a secure change of transmission data with different procedures; after acceptance in the opposite environment, the data is decrypted and restored to its original appearance. Cryptography can solve problems related to network data protection, as well as its successful implementation enabling the protection of applications and data on communication channels, cloud computing, etc. This paper aims to provide an effective cryptographic solution that is sufficient to address issues related to the challenges of transmitting biomedical signals and data (providing protection, preserving the integrity of data, and the confidentiality of patients' personal information). The proposed protection procedure is applied to three types of cardio data: ECG, PPG, and Holter records. All tested signals are real and received with either a PPG device (ECG and PPG) or Holter, which are created or purchased under a research project \"Investigation of the application of new mathematical methods for the analysis of cardiac data\" in which the authors of the paper participated. The implementation of the proposed procedure is implemented in the Microsoft Visual C++ software application. All steps of the procedure have been studied: EPE-based compression algorithm, performing a wavelet transform based on Daubechies, embedding a watermark in the wavelet coefficients obtained at the lowest level of reconstruction, and hybrid algorithm encryption. From the study of algorithmic methods with evaluation parameters, it can be concluded that cardio data (ECG, PPG, and Holter records) that is decrypted and transformed with inverse wavelet transform retain their diagnostic characteristics, having sufficient accuracy compared to the original data. The proposed encryption procedure achieves a good degree of compression, ranging from 3.87 (PPG) to 4.98 (Holter). The Signal to Noise Ratio was examined after applying the encryption algorithm step. The SNR values ranged from 31.83 to 46.37, which is an indicator of the quality of the transmitted signal having been retained. The integrated mathematical approach proposed and researched can be used in the implementation of the protection of the information base from real ECG, PPG, and Holter cardio records, obtained during the authors' work on the research project. The protection of medical signals and patients' personal data can be applied in the transmission of information via communication channels between medical institutions in which records of cardio data are kept and the center for processing and storage of the cardio database. The encryption procedure proposed in this paper will be applied specifically in creating protection for the three types of ECG, PPG, and Holter signals. It involved the implementation of an archive that was processed and tested using mathematical analysis cardio signals obtained in the study of patients with various cardiovascular diseases and a healthy control group. Conceptualization and design, G.B. and G.G.-T.; Data curation and reviews for correctness, G.G.-T. and E.G. ; Conceptualization and methodology for protection of archive from cardio data, [PERSON]; Investigation, [PERSON]-T.; Software creation for mathematical analysis of cardio data, [PERSON]-T.; Performed experiments, [PERSON]-T.; Writing--manuscript, [PERSON]-T.; Manuscript review and contribution to final version, E.G. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Science Fund of Bulgaria (scientific project \"Investigation of the application of new mathematical methods for the analysis of cardiac data\"), Grant Number KP-06-N22/5, 7 December 2018. **Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki, and approved by the Research Ethics Committee at Medical University--Varna, Bulgaria., Protocol/Decision No. 82, 28 March 2019.