Electronic Health Record (EHR) includes highly sensitive data like medical images, prescriptions, medical test result, medical history of patients, etc., these sensitive data cannot be transmitted in its original form in the network due to security issues. Hence, encryption is done prior to transmission. To increase the speed of data transfer and to overcome the storage issues, data is usually transferred through the cloud. Hence, to ensure the security and scalability of the data, a third-party encryption called re-encryption is performed at the proxy cloud. This re-encryption ensures that the data can be reliably transmitted through the network. In this research, a novel scheme called block-chain based EHR data sharing using chaotic re- encryption (BC-EDS-CR) is proposed. In the proposed scheme, re-encryption is performed using chaos theory. The proposed re-encryption scheme ensures that the cloud administrator cannot access the medical data. Metrics such as Peak Signal to Noise Ratio (PSNR), Mean Square Error (MSE), Structural Similarity Index (SSIM), entropy and correlation coefficient are used in evaluating this scheme. It was found that the proposed scheme outperforms the existing methods by achieving a PSNR of 57.66, SSIM of 0.985 and MSE of 0.058.

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