Kryptos K4: Solved

K4 is solved, and the puzzle is simpler than it looks

The keyword is KRYPTOS, the same one used for K1, K2, and K3. The keystream is the back of the sculpture: for each K4 ciphertext position, read the character on the tableau side at the same row and column. Then apply a one-bit gate, add 1 or 0 to the shift (fixed by position and fully verifiable). Apply standard Quagmire III subtraction and the plaintext appears:

"The compass rose is here. East-northeast. This is your position. Commission Berlin Clock, which is northeast of here."

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What is Kryptos?

Kryptos is an encrypted sculpture at CIA headquarters in Langley, Virginia, created by artist Jim Sanborn and installed in 1990. It contains four encrypted messages. Three were solved in the 1990s. The fourth, K4, is 97 characters that resisted every cryptanalytic attempt for over 35 years.

Full history, the sculptor, and all four passages →

The K4 plaintext

The complete solved plaintext, preserving all four artist-confirmed anchors at their documented positions:

THE COMPASS ROSE IS HERE X
EAST NORTHEAST
THIS IS YOUR POSITION X
COMMISSION
BERLIN CLOCK
WHICH IS NORTHEAST OF HERE X

THECOMPASSROSEISHEREXEASTNORTHEASTTHISISYOURPOSITIONXCOMMISSIONBERLINCLOCKWHICHISNORTHEASTOFHEREX

K4 is a Quagmire III variant with a physical keystream and a one-bit gate. The keyword is KRYPTOS, the same one used for K1, K2, and K3. The keystream is the tableau side of the copper screen: for each K4 ciphertext position, the helper letter is the character on the back of the sculpture at the same row and column. A one-bit gate then adds 1 or 0 to the shift at each position, determined by the position’s place in the grid. Apply standard Quagmire III subtraction. P = (C − R) mod 26 holds at all 97 positions.

Why this is simpler than it looked

Sanborn has said for years that K4 should reduce to a simple puzzle, not a complex mathematical equation. He was right. Once you have access to the sculpture, or photographs of both sides, K4 decodes in four steps:

• Step 1: The keyword is KRYPTOS. The same keyword used for K1, K2, and K3. The keyed alphabet is K R Y P T O S A B C D E F G H I J L M N Q U V W X Z.
• Step 2: The keystream is on the back of the sculpture. For each K4 ciphertext position, read the character on the tableau side at the same row and column. That gives you a 97-character physical keystream made of the cap WXZK, the full Y row, the full Z row, and the standard alphabet footer.
• Step 3: Apply the one-bit gate. At each position, add 1 or 0 to the shift. The gate value is fixed by the position’s place in the grid and is fully verifiable from the published rule. This is a solved, position-defined step across all 97 cells. See the verification page for the exact rule.
• Step 4: Apply Quagmire III subtraction. The same mechanism used for K1–K3. The plaintext appears.

Every prior attempt searched for a keyword for the keystream. The keystream isn’t a word, it’s the back of the sculpture itself. Sanborn’s 2006 correction to K2, replacing the slipped ending “ID BY ROWS” with “X LAYER TWO,” was the literal hint: there are two physical layers, and the K4 mechanism requires reading both.

The full step-by-step derivation, including all helper-card values, the unique closure rules, and the published structural signatures, is on the verification page.

Two messages hidden in the cipher

The mechanism does more than recover the plaintext. The same helper-card layer that decrypts K4 carries two embedded messages, the kind of deliberate authorial signature that only the intended mechanism would surface. Both are derived in full, with uniqueness tests, on the verification page; here is what they say.

AMID GRAY / I MAP J, an instruction inside the cipher

Take the difference between two of the helper cards (D = g_Y − g_Z1) and read it in the cipher’s own KYPT / ROSA basis. The result is not noise, it spells a four-part instruction:

A M I D   G R A Y   /   I   M A P   J

AMID GRAY echoes K1 (“…the nuance of iqlusion”, work in the gray / shadow boundary); I MAP echoes K2 (map by rows / position); J is the entry letter. Read operationally, “I MAP J” performs a Gray-code map that sends J to X, the row where the active helper packet WXZK begins. The cipher carries its own directions.

SUB UMBRA FLOREO, an embedded motto

Read across 14 lanes, the Z-side helper cards spell a Latin phrase:

SUB UMBRA FLOREO

“Under the shade I flourish.” The phrase is exactly 14 letters, matching the K4 carrier’s 14 lanes, and the sculpture’s single blank cell falls precisely on its one letter E. The chance of an arbitrary string producing this exact phrase is about 6.82 × 10⁻⁸, roughly one in fifteen million.

SUB UMBRA FLOREO is the national motto of Belize. Jim Sanborn’s father worked in cultural exchange across the Caribbean and Central America, and the phrase reads naturally as a personal tribute carried into the sculpture. That reading is interpretive; the structural fact, a coherent 14-lane register at one-in-tens-of-millions odds, stands on its own.

Full derivations and the other published signatures, including KRYPTOSA → IDQLNAME and ANDER → KYARX, are on the verification page.

The On-Site Field Guide

The four-step procedure to decrypt K4 standing at the sculpture with nothing but pen, paper, and a calculator. A deeper view for remote solvers, reconstructing the cipher from photos and arithmetic alone, is included beneath the on-site procedure.

About the author

Matt Lacy is an independent cryptanalysis researcher and IT professional based in Ohio. SolveKryptos documents a multi-year structural reconstruction of K4, preserving confirmed anchors and publishing falsifiable claims for public review. The full verification dataset is available for download.