page_title: John Herivel
section_title: Herivel tip
hierarchical_section_title: John Herivel / Herivel tip
caption_attribution_description: English: Two Enigma rotors and the spindle on which they are mounted. When the machine is assembled, the spring-loaded studs on the right hand side of rotor (pictured left), make electrical contact with the brass contacts on the left hand side of the rotor (pictured right). The rotor to the left shows the tooth-edged rachet of the stepping mechanism. The notch adjacent to the letter 'D' on the rotor to the right, allows the pawl of the stepping mechanism to fall into place to advance the rotor to its left.
context_page_description: John William Jamieson Herivel was a British science historian and former World War II codebreaker at Bletchley Park.
  As a codebreaker concerned with Cryptanalysis of the Enigma, Herivel is remembered chiefly for the discovery of what was soon dubbed the Herivel tip or Herivelismus. Herivelismus consisted of the idea, the Herivel tip and the method of establishing whether it applied using the Herivel square. It was based on Herivel's insight into the habits of German operators of the Enigma cipher machine that allowed Bletchley Park to easily deduce part of the daily key. For a brief but critical period after May 1940, the Herivel tip in conjunction with "cillies" was the main technique used to solve Enigma.
  After the war, Herivel became an academic, studying the history and philosophy of science at Queen's University Belfast, particularly Isaac Newton, Joseph Fourier, Christiaan Huygens. In retirement, he wrote an autobiographical account of his work at Bletchley Park entitled Herivelismus and the German Military Enigma.
context_section_description: Herivel had an insight in February 1940 that some lazy German code clerks might give away the Enigma's ring settings (Ringstellung) in their first message of the day. If there were several lazy clerks, the first message Grundstellungs would not be random but would have a clustering around the Ringstellung. The insight became known as the Herivel tip. It was not needed at the time because the Luftwaffe was doubly-enciphering their message keys so techniques such as Zygalski sheets could be used. In May 1940, the Germans stopped the doubly-enciphered keys. Other methods becoming ineffective, Bletchley Park started using the Herivel tip to break Luftwaffe traffic. It continued to be the main method until the bombe was delivered in August 1940.
caption: Two Enigma rotors showing electrical contacts, stepping ratchet (on the left) and notch (on the right-hand rotor opposite letter D).
exif: {"Image ImageDescription": "", "Image Make": "Canon", "Image Model": "Canon PowerShot G10", "Image Orientation": "Horizontal (normal)", "Image XResolution": "180", "Image YResolution": "180", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop Elements 6.0 Windows", "Image DateTime": "2011:07:29 18:19:35", "Image YCbCrPositioning": "Co-sited", "Image ExifOffset": "280", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "1202", "Thumbnail JPEGInterchangeFormatLength": "4750", "EXIF ExposureTime": "1/8", "EXIF FNumber": "9/2", "EXIF ISOSpeedRatings": "320", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2011:07:22 10:51:55", "EXIF DateTimeDigitized": "2011:07:22 10:51:55", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "5", "EXIF ShutterSpeedValue": "3", "EXIF ApertureValue": "139/32", "EXIF ExposureBiasValue": "-5/3", "EXIF MaxApertureValue": "139/32", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "12489/500", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "3134", "EXIF ExifImageLength": "1662", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "Interoperability RelatedImageWidth": "4416", "Interoperability RelatedImageLength": "3312", "EXIF InteroperabilityOffset": "1052", "EXIF FocalPlaneXResolution": "1104000/73", "EXIF FocalPlaneYResolution": "1104000/73", "EXIF FocalPlaneResolutionUnit": "2", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Manual Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF SceneCaptureType": "Standard"}