A system, comprising: a client device comprising at least one hardware processor; a client application executable in the client device comprising program instructions that, when executed, cause the client device to: generate a first machine-readable identifier using a first amount of data encrypted using at least one cryptographic key for rendering in a display of the client device, wherein a reader device having the at least one cryptographic key stored thereon is configured to decrypt the first amount of data, the first amount of data comprising a first portion of user input and a second portion of user input, the first portion of user input being encrypted using a first cryptographic key that is accessible by the reader device and the second portion of user input being encrypted using a second cryptographic key that is inaccessible by the reader device; identify a second machine-readable identifier in at least one image captured by the client device, the second machine-readable identifier being generated by the reader device; decode the second machine-readable identifier to identify a second amount of data created by the reader device, after the first amount of data is decrypted using the at least one cryptographic key, based at least in part on the first amount of data and encrypted by the reader device using the at least one cryptographic key; decrypt the second amount of data using the at least one cryptographic key; and identify whether a conflict exists between the first amount of data and the second amount of data. a client device comprising at least one hardware processor; a client application executable in the client device comprising program instructions that, when executed, cause the client device to: generate a first machine-readable identifier using a first amount of data encrypted using at least one cryptographic key for rendering in a display of the client device, wherein a reader device having the at least one cryptographic key stored thereon is configured to decrypt the first amount of data, the first amount of data comprising a first portion of user input and a second portion of user input, the first portion of user input being encrypted using a first cryptographic key that is accessible by the reader device and the second portion of user input being encrypted using a second cryptographic key that is inaccessible by the reader device; identify a second machine-readable identifier in at least one image captured by the client device, the second machine-readable identifier being generated by the reader device; decode the second machine-readable identifier to identify a second amount of data created by the reader device, after the first amount of data is decrypted using the at least one cryptographic key, based at least in part on the first amount of data and encrypted by the reader device using the at least one cryptographic key; decrypt the second amount of data using the at least one cryptographic key; and identify whether a conflict exists between the first amount of data and the second amount of data. generate a first machine-readable identifier using a first amount of data encrypted using at least one cryptographic key for rendering in a display of the client device, wherein a reader device having the at least one cryptographic key stored thereon is configured to decrypt the first amount of data, the first amount of data comprising a first portion of user input and a second portion of user input, the first portion of user input being encrypted using a first cryptographic key that is accessible by the reader device and the second portion of user input being encrypted using a second cryptographic key that is inaccessible by the reader device; identify a second machine-readable identifier in at least one image captured by the client device, the second machine-readable identifier being generated by the reader device; decode the second machine-readable identifier to identify a second amount of data created by the reader device, after the first amount of data is decrypted using the at least one cryptographic key, based at least in part on the first amount of data and encrypted by the reader device using the at least one cryptographic key; decrypt the second amount of data using the at least one cryptographic key; and identify whether a conflict exists between the first amount of data and the second amount of data.