The Enigma machine was one of only two in the world
Second World War memorabilia dealer Dennis Yates, 58, from Sandiacre, Nottinghamshire, was sentenced at Aylesbury Crown Court on Friday.
At a previous hearing he admitted handling the £100,000 machine between 31 March 2000 and 19 November 2000.
The encoding machine was stolen from a display cabinet at Bletchley Park - codenamed Station X - on 1 April last year during an open day at the former top secret site.
Following months of ransom demands, the machine, one of only three left in the world, was returned via BBC Two's Newsnight presenter Jeremy Paxman.
'Honest broker'
Yates was eventually arrested at a phone box in Leicestershire last November, making a phone call to a national newspaper through which many negotiations between Yates and the police were conducted.
He maintained he had only acted as an "honest broker" for an unnamed buyer in India, referred to as "The Master", and had no knowledge of the theft of the encoding machine.
From his cell during questioning, he negotiated the safe return of three rotors, essential for the machine to work properly.
He admitted at the hearing on 26 September that he had written a series of letters to Christine Large, the director of Bletchley Park, following the disappearance of the machine, demanding a £25,000 ransom for its safe return and threatening to destroy it unless the ransom was paid.
Before he was sentenced, Yates said: "I feel I have been treated fairly but it was just unfortunate circumstances I got myself involved in and in retrospect, I would have run away."
Death threats
Rupert Pardoe, defending, said: "The greatest mitigation this man has is that he pleaded guilty.
"He has no previous convictions and his plea of guilty showed the greatest courage.
"The defendant is adamant, and remains adamant, that the machine would be returned and he always intended its repatriation.
"He became massively out of his depth in an event which spiralled out of his control."
The court was also played recorded death threats from an unidentified caller warning Yates to "keep his mouth shut" or he would "end up in the ground", which Mr Pardoe said may explain why he never named to police the purchaser of the Enigma machine.
Sentencing him to 10 months in jail, Judge Daniel Rodwell said: "By your plea, you have admitted that you knew that this machine was stolen and it was dishonest of you to receive it.
"This was premeditated dishonesty which went on for a long period of time.
"You had the expertise to know exactly what this machine was - an extremely rare example of a four-rotor Enigma, of which there are only two in the world, and a very important part of our national heritage."