diff --git a/DESCRIPTION b/DESCRIPTION
index 8b86557..20d0393 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -5,8 +5,11 @@ Version: 0.2.0.9000
 Description: SHA-256, SHA-3 cryptographic hash and SHAKE256 extendable-output
     functions (XOF). The SHA-3 Secure Hash Standard was published by the
     National Institute of Standards and Technology (NIST) in 2015 at
-    <doi:10.6028/NIST.FIPS.202>. Fast and memory-efficient implementation using
-    the core algorithms from 'Mbed TLS' under the Trusted Firmware Project
+    <doi:10.6028/NIST.FIPS.202>. The SHA-256 Secure Hash Standard was published
+    by NIST in 2002 at
+    <https://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>. Fast and
+    memory-efficient implementation using the core algorithms from 'Mbed TLS'
+    under the Trusted Firmware Project
     <https://www.trustedfirmware.org/projects/mbed-tls/>.
 Authors@R: 
     c(person(given = "Charlie",
diff --git a/README.Rmd b/README.Rmd
index 7d427b4..62c012b 100644
--- a/README.Rmd
+++ b/README.Rmd
@@ -25,7 +25,8 @@ knitr::opts_chunk$set(
 
 SHA-256, SHA-3 cryptographic hash and SHAKE256 extendable-output functions (XOF).
 
-The SHA-3 Secure Hash Standard was published by the National Institute of Standards and Technology (NIST) in 2015 at [doi:10.6028/NIST.FIPS.202](https://dx.doi.org/10.6028/NIST.FIPS.202).
+The SHA-3 Secure Hash Standard was published by the National Institute of Standards and Technology (NIST) in 2015 at [doi:10.6028/NIST.FIPS.202](https://dx.doi.org/10.6028/NIST.FIPS.202). The SHA-256 Secure Hash Standard was published by NIST in 2002 at <https://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>.
+
 
 Fast and memory-efficient implementation using the core algorithms from 'Mbed TLS' under the Trusted Firmware Project <https://www.trustedfirmware.org/projects/mbed-tls/>.
 
diff --git a/README.md b/README.md
index 933e51d..ee8f2f2 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,8 @@ functions (XOF).
 The SHA-3 Secure Hash Standard was published by the National Institute
 of Standards and Technology (NIST) in 2015 at
 [doi:10.6028/NIST.FIPS.202](https://dx.doi.org/10.6028/NIST.FIPS.202).
+The SHA-256 Secure Hash Standard was published by NIST in 2002 at
+<https://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>.
 
 Fast and memory-efficient implementation using the core algorithms from
 ‘Mbed TLS’ under the Trusted Firmware Project