Datasheet

Table Of Contents

• Generally, u2ScalarLength is equal to (u2ModLength) or (u2ModLength + 4)

Important:

For the ECDSA signature generation be sure to follow the directives given for the RNG on the

chip you use (particularly initialization, seeding) and compulsorily start the RNG.

The scalar number k must be selected at random. This random must be generated before the

call of the ECDSA signature. For this random generation be sure to follow the directives given

for the RNG on the chip you use (particularly initialization, seeding) and compulsorily start the

RNG.

The operation performed is:

• Compute the ECDSA (R,S) as described in FIPS 186-2, but leaving the user the role of computing

the input Hash Value, thus leaving the freedom of using any other algorithm than SHA-1.

• Compute a R value using the input A point and the scalar number.

• Compute a S value using R, the scalar number, the private key and the provided hash value. Note

that the resulting signature (R,S) is stored at the place of the input A point.

• If all is correct and S is different from zero, the status is set to PUKCL_OK. If all is correct and S

equals zero,the status is set to PUKCL_WRONG_SELECT_NUMBER. If an error occurs, the status

is set to the corresponding error value (see Status Returned Values below).

The service name for this operation is ZpEcDsaGenerateFast. This service uses Fast mode and Fast

Modular Reduction for computation.

• The signature (R,S), when resulting from a computation is given back at address of the A point:

– R output is at offset 0 and has length (u2ScalarLength + 4)bytes.

– S output is at offset (u2ScalarLength + 4) bytes and has length (u2ScalarLength + 4) bytes.

– The MSB 4 zero bytes may be suppressed to get the R and S values on u2ScalarLength bytes

SAM D5x/E5x Family Data Sheet

Public Key Cryptography Controller (PUKCC)

Datasheet

DS60001507E-page 1532