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Provided are a data transmission method, apparatus and system. The method comprises: generating an asymmetrical secret key pair comprising a first public key and a first private key, and sending a data request carrying the first public key to a server end; receiving a ciphertext and a second public key sent by the server end, wherein the second public key is a public key in the asymmetrical secret key pair acquired by the server end, the asymmetrical secret key pair acquired by the server end also comprises a second private key, the ciphertext is information after encrypting a seed parameter for generating an offline payment code by using a shared secret key, and the shared secret key is a secret key generated by using a pre-set secret key negotiation algorithm according to the second private key and the first public key; and according to the first private key and the second public key, generating the shared secret key by using the secret key negotiation algorithm, and using the shared secret key to decrypt the ciphertext so as to obtain the seed parameter. The present application not only ensures data security during the whole transmission process, but also improves encryption and decryption efficiency.