An electronic system (100; 200) for generating a cryptographic key, the system comprising - a memory used as a physically unclonable function, the memory being writable, volatile and configured such that upon each powering-up of the memory the memory settles into a memory content which depends upon at least partially random physical characteristics of the memory, the memory being accessible through a memory interface, and - a key derivation unit (150; 230) configured to derive the cryptographic key from the memory content into which the memory settled, wherein the electronic system for generating a cryptographic key further comprises, - a memory read-out unit connected to the memory through the memory interface and to the key derivation unit, the memory read-out unit comprising - an address scrambler for retrieving the memory content over the memory interface in a scrambled order, and an address generator for retrieving the memory content in a pre-determined further order, wherein the scrambled order is derived from a seed at least partially randomly generated after each power-up of the read-out unit, - an encryption unit for encrypting the memory with a temporary key, the encryption unit being configured to receive from the memory interface the memory content retrieved by the address scrambler in the scrambled order, encrypt the received memory content and write back the encrypted memory content to the memory, and - a decryption unit for decrypting the memory, configured to receive from the memory interface the encrypted memory content retrieved by the address generator in the pre-determined further order, decrypt the received encrypted memory content to obtain the memory content in the pre-determined further order, wherein read-out of the memory for the key derivation unit is done in two passes, in a first pass the memory is encrypted, wherein access to the memory is in a scrambled order, and in a second pass the memory is read-out in the pre-determined order, wherein data that passes over the memory interface is encrypted. - a memory used as a physically unclonable function, the memory being writable, volatile and configured such that upon each powering-up of the memory the memory settles into a memory content which depends upon at least partially random physical characteristics of the memory, the memory being accessible through a memory interface, and - a key derivation unit (150; 230) configured to derive the cryptographic key from the memory content into which the memory settled, wherein the electronic system for generating a cryptographic key further comprises, - a memory read-out unit connected to the memory through the memory interface and to the key derivation unit, the memory read-out unit comprising - an address scrambler for retrieving the memory content over the memory interface in a scrambled order, and an address generator for retrieving the memory content in a pre-determined further order, wherein the scrambled order is derived from a seed at least partially randomly generated after each power-up of the read-out unit, - an encryption unit for encrypting the memory with a temporary key, the encryption unit being configured to receive from the memory interface the memory content retrieved by the address scrambler in the scrambled order, encrypt the received memory content and write back the encrypted memory content to the memory, and - a decryption unit for decrypting the memory, configured to receive from the memory interface the encrypted memory content retrieved by the address generator in the pre-determined further order, decrypt the received encrypted memory content to obtain the memory content in the pre-determined further order, wherein read-out of the memory for the key derivation unit is done in two passes, in a first pass the memory is encrypted, wherein access to the memory is in a scrambled order, and in a second pass the memory is read-out in the pre-determined order, wherein data that passes over the memory interface is encrypted. - an address scrambler for retrieving the memory content over the memory interface in a scrambled order, and an address generator for retrieving the memory content in a pre-determined further order, wherein the scrambled order is derived from a seed at least partially randomly generated after each power-up of the read-out unit, - an encryption unit for encrypting the memory with a temporary key, the encryption unit being configured to receive from the memory interface the memory content retrieved by the address scrambler in the scrambled order, encrypt the received memory content and write back the encrypted memory content to the memory, and - a decryption unit for decrypting the memory, configured to receive from the memory interface the encrypted memory content retrieved by the address generator in the pre-determined further order, decrypt the received encrypted memory content to obtain the memory content in the pre-determined further order,